CKS练习题

2023-12-23 / 0 评论 / 74 阅读 / 正在检测是否收录...

Pre Setup

Once you've gained access to your terminal it might be wise to spend ~1 minute to setup your environment. You could set these:

alias k=kubectl                         # will already be pre-configured

export do="--dry-run=client -o yaml"    # k create deploy nginx --image=nginx $do

export now="--force --grace-period 0"   # k delete pod x $now

The following settings will already be configured in your real exam environment in ~/.vimrc. But it can never hurt to be able to type these down:

set tabstop=2
set expandtab
set shiftwidth=2

More setup suggestions are in the tips section.

第一题:Contexts

问题

Task weight: 1%

You have access to multiple clusters from your main terminal through kubectlcontexts. Write all context names into  /opt/course/1/contexts, one per line.

From the kubeconfig extract the certificate of user restricted@infra-prodand write it decoded to /opt/course/1/cert.

解答1

kubectl config get-contexts -o name > /opt/course/1/contexts
kubectl config view --raw -o jsonpath='{.users[?(@name == "restricted@infra-prod")].user.client-certificate-data}' | base64 -d > /opt/course/1/cert

解答2

Answer:
Maybe the fastest way is just to run:

k config get-contexts # copy by hand

k config get-contexts -o name > /opt/course/1/contexts

Or using jsonpath:

k config view -o jsonpath="{.contexts[*].name}"
k config view -o jsonpath="{.contexts[*].name}" | tr " " "\n" # new lines
k config view -o jsonpath="{.contexts[*].name}" | tr " " "\n" > /opt/course/1/contexts

The content could then look like:

# /opt/course/1/contexts
gianna@infra-prod
infra-prod
restricted@infra-prod
workload-prod
workload-stage

For the certificate we could just run

k config view --raw

And copy it manually. Or we do:

k config view --raw -ojsonpath="{.users[2].user.client-certificate-data}" | base64 -d > /opt/course/1/cert

Or even:

k config view --raw -ojsonpath="{.users[?(.name == 'restricted@infra-prod')].user.client-certificate-data}" | base64 -d > /opt/course/1/cert
# /opt/course/1/cert
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

第二题: Runtime Security with Falco

问题

Task weight: 4%

Use context: kubectl config use-context workload-prod

Falco is installed with default configuration on node cluster1-node1. Connect using ssh cluster1-node1. Use it to:

Find a Pod running image nginx which creates unwanted package management processes inside its container.

Find a Pod running image httpd which modifies /etc/passwd.

Save the Falco logs for case 1 under /opt/course/2/falco.log in format:

time-with-nanosconds,container-id,container-name,user-name

No other information should be in any line. Collect the logs for at least 30 seconds.

Afterwards remove the threads (both 1 and 2) by scaling the replicas of the Deployments that control the offending Pods down to 0.

解答:

Use Falco as service

First we can investigate Falco config a little:

➜ ssh cluster1-node1

➜ root@cluster1-node1:~# service falco status
● falco.service - LSB: Falco syscall activity monitoring agent
   Loaded: loaded (/etc/init.d/falco; generated)
   Active: active (running) since Sat 2020-10-10 06:36:15 UTC; 2h 1min ago
...

➜ root@cluster1-node1:~# cd /etc/falco

➜ root@cluster1-node1:/etc/falco# ls
falco.yaml  falco_rules.local.yaml  falco_rules.yaml  k8s_audit_rules.yaml  rules.available  rules.d

This is the default configuration, if we look into falco.yaml we can see:

# /etc/falco/falco.yaml

...
# Where security notifications should go.
# Multiple outputs can be enabled.

syslog_output:
  enabled: true
...

This means that Falco is writing into syslog, hence we can do:

➜ root@cluster1-node1:~# cat /var/log/syslog | grep falco
Sep 15 08:44:04 ubuntu2004 falco: Falco version 0.29.1 (driver version 17f5df52a7d9ed6bb12d3b1768460def8439936d)
Sep 15 08:44:04 ubuntu2004 falco: Falco initialized with configuration file /etc/falco/falco.yaml
Sep 15 08:44:04 ubuntu2004 falco: Loading rules from file /etc/falco/falco_rules.yaml:
...

Yep, quite some action going on in there. Let's investigate the first offending Pod:

➜ root@cluster1-node1:~# cat /var/log/syslog | grep falco | grep nginx | grep process
Sep 16 06:23:47 ubuntu2004 falco: 06:23:47.376241377: Error Package management process launched in container (user=root user_loginuid=-1 command=apk container_id=7a5ea6a080d1 container_name=nginx image=docker.io/library/nginx:1.19.2-alpine)
...

➜ root@cluster1-node1:~# crictl ps -id 7a5ea6a080d1
CONTAINER ID        IMAGE              NAME        ...         POD ID
7a5ea6a080d1b       6f715d38cfe0e      nginx       ...         7a864406b9794

root@cluster1-node1:~# crictl pods -id 7a864406b9794
POD ID              ...          NAME                             NAMESPACE        ...
7a864406b9794       ...          webapi-6cfddcd6f4-ftxg4          team-blue        ...

First Pod is webapi-6cfddcd6f4-ftxg4 in Namespace team-blue.

➜ root@cluster1-node1:~# cat /var/log/syslog | grep falco | grep httpd | grep passwd
Sep 16 06:23:48 ubuntu2004 falco: 06:23:48.830962378: Error File below /etc opened for writing (user=root user_loginuid=-1 command=sed -i $d /etc/passwd parent=sh pcmdline=sh -c echo hacker >> /etc/passwd; sed -i '$d' /etc/passwd; true file=/etc/passwdngFmAl program=sed gparent=<NA> ggparent=<NA> gggparent=<NA> container_id=b1339d5cc2de image=docker.io/library/httpd)

➜ root@cluster1-node1:~# crictl ps -id b1339d5cc2de
CONTAINER ID        IMAGE              NAME        ...         POD ID
b1339d5cc2dee       f6b40f9f8ad71      httpd       ...         595af943c3245

root@cluster1-node1:~# crictl pods -id 595af943c3245
POD ID              ...          NAME                             NAMESPACE          ...
595af943c3245       ...          rating-service-68cbdf7b7-v2p6g   team-purple        ...

Second Pod is rating-service-68cbdf7b7-v2p6g in Namespace team-purple.

Eliminate offending Pods

The logs from before should allow us to find and "eliminate" the offending Pods:

➜ k get pod -A | grep webapi
team-blue              webapi-6cfddcd6f4-ftxg4                      1/1     Running 

➜ k -n team-blue scale deploy webapi --replicas 0
deployment.apps/webapi scaled

➜ k get pod -A | grep rating-service
team-purple            rating-service-68cbdf7b7-v2p6g               1/1     Running

➜ k -n team-purple scale deploy rating-service --replicas 0
deployment.apps/rating-service scaled

Use Falco from command line

We can also use Falco directly from command line, but only if the service is disabled:

➜ root@cluster1-node1:~# service falco stop

➜ root@cluster1-node1:~# falco
Thu Sep 16 06:33:11 2021: Falco version 0.29.1 (driver version 17f5df52a7d9ed6bb12d3b1768460def8439936d)
Thu Sep 16 06:33:11 2021: Falco initialized with configuration file /etc/falco/falco.yaml
Thu Sep 16 06:33:11 2021: Loading rules from file /etc/falco/falco_rules.yaml:
Thu Sep 16 06:33:11 2021: Loading rules from file /etc/falco/falco_rules.local.yaml:
Thu Sep 16 06:33:11 2021: Loading rules from file /etc/falco/k8s_audit_rules.yaml:
Thu Sep 16 06:33:12 2021: Starting internal webserver, listening on port 8765
06:33:17.382603204: Error Package management process launched in container (user=root user_loginuid=-1 command=apk container_id=7a5ea6a080d1 container_name=nginx image=docker.io/library/nginx:1.19.2-alpine)
...

We can see that rule files are loaded and logs printed afterwards.

Create logs in correct format

The task requires us to store logs for "unwanted package management processes" in format time,container-id,container-name,user-name. The output from falco shows entries for "Error Package management process launched" in a default format. Let's find the proper file that contains the rule and change it:

➜ root@cluster1-node1:~# cd /etc/falco/

➜ root@cluster1-node1:/etc/falco# grep -r "Package management process launched" .
./falco_rules.yaml:    Package management process launched in container (user=%user.name user_loginuid=%user.loginuid

➜ root@cluster1-node1:/etc/falco# cp falco_rules.yaml falco_rules.yaml_ori

➜ root@cluster1-node1:/etc/falco# vim falco_rules.yaml

Find the rule which looks like this:

# Container is supposed to be immutable. Package management should be done in building the image.
- rule: Launch Package Management Process in Container
  desc: Package management process ran inside container
  condition: >
    spawned_process
    and container
    and user.name != "_apt"
    and package_mgmt_procs
    and not package_mgmt_ancestor_procs
    and not user_known_package_manager_in_container
  output: >
    Package management process launched in container (user=%user.name user_loginuid=%user.loginuid
    command=%proc.cmdline container_id=%container.id container_name=%container.name image=%container.image.repository:%container.image.tag)
  priority: ERROR
  tags: [process, mitre_persistence]

Should be changed into the required format (在local.yaml文件中覆盖这条规则更好):

# Container is supposed to be immutable. Package management should be done in building the image.
- rule: Launch Package Management Process in Container
  desc: Package management process ran inside container
  condition: >
    spawned_process
    and container
    and user.name != "_apt"
    and package_mgmt_procs
    and not package_mgmt_ancestor_procs
    and not user_known_package_manager_in_container
  output: >
    Package management process launched in container %evt.time,%container.id,%container.name,%user.name
  priority: ERROR
  tags: [process, mitre_persistence]

For all available fields we can check
https://falco.org/docs/rules/supported-fields, which should be allowed to open during the exam.

Next we check the logs in our adjusted format:

➜ root@cluster1-node1:/etc/falco# falco | grep "Package management"

06:38:28.077150666: Error Package management process launched in container 06:38:28.077150666,090aad374a0a,nginx,root
06:38:33.058263010: Error Package management process launched in container 06:38:33.058263010,090aad374a0a,nginx,root
06:38:38.068693625: Error Package management process launched in container 06:38:38.068693625,090aad374a0a,nginx,root
06:38:43.066159360: Error Package management process launched in container 06:38:43.066159360,090aad374a0a,nginx,root
06:38:48.059792139: Error Package management process launched in container 06:38:48.059792139,090aad374a0a,nginx,root
06:38:53.063328933: Error Package management process launched in container 06:38:53.063328933,090aad374a0a,nginx,root

This looks much better. Copy&paste the output into file /opt/course/2/falco.log on your main terminal. The content should be cleaned like this:

# /opt/course/2/falco.log
06:38:28.077150666,090aad374a0a,nginx,root
06:38:33.058263010,090aad374a0a,nginx,root
06:38:38.068693625,090aad374a0a,nginx,root
06:38:43.066159360,090aad374a0a,nginx,root
06:38:48.059792139,090aad374a0a,nginx,root
06:38:53.063328933,090aad374a0a,nginx,root
06:38:58.070912841,090aad374a0a,nginx,root
06:39:03.069592140,090aad374a0a,nginx,root
06:39:08.064805371,090aad374a0a,nginx,root
06:39:13.078109098,090aad374a0a,nginx,root
06:39:18.065077287,090aad374a0a,nginx,root
06:39:23.061012151,090aad374a0a,nginx,root

For a few entries it should be fast to just clean it up manually. If there are larger amounts of entries we could do(现将日志重定向保存到/opt/course/2/falco.log.dirty, 然后使用以下命令更快):

cat /opt/course/2/falco.log.dirty | cut -d" " -f 9 > /opt/course/2/falco.log

Local falco rules

There is also a file /etc/falco/falco_rules.local.yaml in which we can override existing default rules. This is a much cleaner solution for production. Choose the faster way for you in the exam if nothing is specified in the task.

第三题: Apiserver Security

问题

Task weight: 3%

Use context: kubectl config use-context workload-prod

You received a list from the DevSecOps team which performed a security investigation of the k8s cluster1 (workload-prod). The list states the following about the apiserver setup:

  • Accessible through a NodePort Service

Change the apiserver setup so that:

  • Only accessible through a ClusterIP Service

解答

In order to modify the parameters for the apiserver, we first ssh into the master node and check which parameters the apiserver process is running with:

➜ ssh cluster1-controlplane1

➜ root@cluster1-controlplane1:~# ps aux | grep kube-apiserver
root       27622  7.4 15.3 1105924 311788 ?      Ssl  10:31  11:03 kube-apiserver --advertise-address=192.168.100.11 --allow-privileged=true --authorization-mode=Node,RBAC --client-ca-file=/etc/kubernetes/pki/ca.crt --enable-admission-plugins=NodeRestriction --enable-bootstrap-token-auth=true --etcd-cafile=/etc/kubernetes/pki/etcd/ca.crt --etcd-certfile=/etc/kubernetes/pki/apiserver-etcd-client.crt --etcd-keyfile=/etc/kubernetes/pki/apiserver-etcd-client.key --etcd-servers=https://127.0.0.1:2379 --kubelet-client-certificate=/etc/kubernetes/pki/apiserver-kubelet-client.crt --kubelet-client-key=/etc/kubernetes/pki/apiserver-kubelet-client.key --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname --kubernetes-service-node-port=31000 --proxy-client-cert-
...

We may notice the following argument:

--kubernetes-service-node-port=31000

We can also check the Service and see it's of type NodePort:

➜ root@cluster1-controlplane1:~# kubectl get svc
NAME         TYPE       CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
kubernetes   NodePort   10.96.0.1    <none>        443:31000/TCP   5d2h

The apiserver runs as a static Pod, so we can edit the manifest. But before we do this we also create a copy in case we mess things up:

➜ root@cluster1-controlplane1:~# cp /etc/kubernetes/manifests/kube-apiserver.yaml ~/3_kube-apiserver.yaml

➜ root@cluster1-controlplane1:~# vim /etc/kubernetes/manifests/kube-apiserver.yaml

We should remove the unsecure settings:

# /etc/kubernetes/manifests/kube-apiserver.yaml
apiVersion: v1
kind: Pod
metadata:
  annotations:
    kubeadm.kubernetes.io/kube-apiserver.advertise-address.endpoint: 192.168.100.11:6443
  creationTimestamp: null
  labels:
    component: kube-apiserver
    tier: control-plane
  name: kube-apiserver
  namespace: kube-system
spec:
  containers:
  - command:
    - kube-apiserver
    - --advertise-address=192.168.100.11
    - --allow-privileged=true
    - --authorization-mode=Node,RBAC
    - --client-ca-file=/etc/kubernetes/pki/ca.crt
    - --enable-admission-plugins=NodeRestriction
    - --enable-bootstrap-token-auth=true
    - --etcd-cafile=/etc/kubernetes/pki/etcd/ca.crt
    - --etcd-certfile=/etc/kubernetes/pki/apiserver-etcd-client.crt
    - --etcd-keyfile=/etc/kubernetes/pki/apiserver-etcd-client.key
    - --etcd-servers=https://127.0.0.1:2379
    - --kubelet-client-certificate=/etc/kubernetes/pki/apiserver-kubelet-client.crt
    - --kubelet-client-key=/etc/kubernetes/pki/apiserver-kubelet-client.key
    - --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
# 注释这里,或者设置成0
#    - --kubernetes-service-node-port=31000   # delete or set to 0
    - --proxy-client-cert-file=/etc/kubernetes/pki/front-proxy-client.crt
    - --proxy-client-key-file=/etc/kubernetes/pki/front-proxy-client.key
...

Once the changes are made, give the apiserver some time to start up again. Check the apiserver's Pod status and the process parameters:

➜ root@cluster1-controlplane1:~# kubectl -n kube-system get pod | grep apiserver
kube-apiserver-cluster1-controlplane1            1/1     Running        0          38s

➜ root@cluster1-controlplane1:~# ps aux | grep kube-apiserver | grep node-port

The apiserver got restarted without the unsecure settings. However, the Service kubernetes will still be of type NodePort:

➜ root@cluster1-controlplane1:~# kubectl get svc
NAME         TYPE       CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
kubernetes   NodePort   10.96.0.1    <none>        443:31000/TCP   5d3h

We need to delete the Service for the changes to take effect:

➜ root@cluster1-controlplane1:~# kubectl delete svc kubernetes
service "kubernetes" deleted

After a few seconds:

➜ root@cluster1-controlplane1:~# kubectl get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   6s

This should satisfy the DevSecOps team.

第四题: Pod Security Standard

问题

ask weight: 8%

Use context: kubectl config use-context workload-prod

There is Deployment container-host-hacker in Namespace team-red which mounts /run/containerd as a hostPath volume on the Node where it's running. This means that the Pod can access various data about other containers running on the same Node.

To prevent this configure Namespace team-red to enforce the baseline Pod Security Standard. Once completed, delete the Pod of the Deployment mentioned above.

Check the ReplicaSet events and write the event/log lines containing the reason why the Pod isn't recreated into /opt/course/4/logs.

解答

Making Namespaces use Pod Security Standards works via labels. We can simply edit it:

k edit ns team-red

ow we configure the requested label:

# kubectl edit namespace team-red
apiVersion: v1
kind: Namespace
metadata:
  labels:
    kubernetes.io/metadata.name: team-red
    pod-security.kubernetes.io/enforce: baseline # add
  name: team-red
...

This should already be enough for the default Pod Security Admission Controller to pick up on that change. Let's test it and delete the Pod to see if it'll be recreated or fails, it should fail!

➜ k -n team-red get pod
NAME                                    READY   STATUS    RESTARTS   AGE
container-host-hacker-dbf989777-wm8fc   1/1     Running   0          115s

➜ k -n team-red delete pod container-host-hacker-dbf989777-wm8fc 
pod "container-host-hacker-dbf989777-wm8fc" deleted

➜ k -n team-red get pod
No resources found in team-red namespace.

Usually the ReplicaSet of a Deployment would recreate the Pod if deleted, here we see this doesn't happen. Let's check why:

➜ k -n team-red get rs
NAME                              DESIRED   CURRENT   READY   AGE
container-host-hacker-dbf989777   1         0         0       5m25s

➜ k -n team-red describe rs container-host-hacker-dbf989777
Name:           container-host-hacker-dbf989777
Namespace:      team-red
...
Events:
  Type     Reason            Age                   From                   Message
  ----     ------            ----                  ----                   -------
...
  Warning  FailedCreate      2m41s                 replicaset-controller  Error creating: pods "container-host-hacker-dbf989777-bjwgv" is forbidden: violates PodSecurity "baseline:latest": hostPath volumes (volume "containerdata")
  Warning  FailedCreate      2m2s (x9 over 2m40s)  replicaset-controller  (combined from similar events): Error creating: pods "container-host-hacker-dbf989777-kjfpn" is forbidden: violates PodSecurity "baseline:latest": hostPath volumes (volume "containerdata")

There we go! Finally we write the reason into the requested file so that Mr Scoring will be happy too!

# /opt/course/4/logs
Warning  FailedCreate      2m2s (x9 over 2m40s)  replicaset-controller  (combined from similar events): Error creating: pods "container-host-hacker-dbf989777-kjfpn" is forbidden: violates PodSecurity "baseline:latest": hostPath volumes (volume "containerdata")

od Security Standards can give a great base level of security! But when one finds themselves wanting to deeper adjust the levels like baseline or restricted... this isn't possible and 3rd party solutions like OPA could be looked at.

第五题: CIS Benchmark

问题

Task weight: 3%

Use context: kubectl config use-context infra-prod

You're ask to evaluate specific settings of cluster2 against the CIS Benchmark recommendations. Use the tool kube-bench which is already installed on the nodes.

Connect using ssh cluster2-controlplane1 and ssh cluster2-node1.

On the master node ensure (correct if necessary) that the CIS recommendations are set for:

  1. The--profiling` argument of the kube-controller-manager
  2. The ownership of directory /var/lib/etcd

On the worker node ensure (correct if necessary) that the CIS recommendations are set for:

  1. The permissions of the kubelet configuration /var/lib/kubelet/config.yaml
  2. The --client-ca-file argument of the kubelet

解答

Number 1

First we ssh into the master node run kube-bench against the master components:

➜ ssh cluster2-controlplane1

➜ root@cluster2-controlplane1:~# kube-bench run --targets=master
...
== Summary ==
41 checks PASS
13 checks FAIL
11 checks WARN
0 checks INFO

We see some passes, fails and warnings. Let's check the required task (1) of the controller manager:

➜ root@cluster2-controlplane1:~# kube-bench run --targets=master | grep kube-controller -A 3
1.3.1 Edit the Controller Manager pod specification file /etc/kubernetes/manifests/kube-controller-manager.yaml
on the master node and set the --terminated-pod-gc-threshold to an appropriate threshold,
for example:
--terminated-pod-gc-threshold=10
--
1.3.2 Edit the Controller Manager pod specification file /etc/kubernetes/manifests/kube-controller-manager.yaml
on the master node and set the below parameter.
--profiling=false

1.3.6 Edit the Controller Manager pod specification file /etc/kubernetes/manifests/kube-controller-manager.yaml
on the master node and set the --feature-gates parameter to include RotateKubeletServerCertificate=true.
--feature-gates=RotateKubeletServerCertificate=true

There we see 1.3.2 which suggests to set --profiling=false, so we obey:

➜ root@cluster2-controlplane1:~# vim /etc/kubernetes/manifests/kube-controller-manager.yaml

Edit the corresponding line:

# /etc/kubernetes/manifests/kube-controller-manager.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    component: kube-controller-manager
    tier: control-plane
  name: kube-controller-manager
  namespace: kube-system
spec:
  containers:
  - command:
    - kube-controller-manager
    - --allocate-node-cidrs=true
    - --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
    - --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
    - --bind-address=127.0.0.1
    - --client-ca-file=/etc/kubernetes/pki/ca.crt
    - --cluster-cidr=10.244.0.0/16
    - --cluster-name=kubernetes
    - --cluster-signing-cert-file=/etc/kubernetes/pki/ca.crt
    - --cluster-signing-key-file=/etc/kubernetes/pki/ca.key
    - --controllers=*,bootstrapsigner,tokencleaner
    - --kubeconfig=/etc/kubernetes/controller-manager.conf
    - --leader-elect=true
    - --node-cidr-mask-size=24
    - --port=0
    - --requestheader-client-ca-file=/etc/kubernetes/pki/front-proxy-ca.crt
    - --root-ca-file=/etc/kubernetes/pki/ca.crt
    - --service-account-private-key-file=/etc/kubernetes/pki/sa.key
    - --service-cluster-ip-range=10.96.0.0/12
    - --use-service-account-credentials=true
    - --profiling=false            # add
...

We wait for the Pod to restart, then run kube-bench again to check if the problem was solved:

➜ root@cluster2-controlplane1:~# kube-bench run --targets=master | grep kube-controller -A 3
1.3.1 Edit the Controller Manager pod specification file /etc/kubernetes/manifests/kube-controller-manager.yaml
on the master node and set the --terminated-pod-gc-threshold to an appropriate threshold,
for example:
--terminated-pod-gc-threshold=10
--
1.3.6 Edit the Controller Manager pod specification file /etc/kubernetes/manifests/kube-controller-manager.yaml
on the master node and set the --feature-gates parameter to include RotateKubeletServerCertificate=true.
--feature-gates=RotateKubeletServerCertificate=true

Problem solved and 1.3.2 is passing:

root@cluster2-controlplane1:~# kube-bench run --targets=master | grep 1.3.2
[PASS] 1.3.2 Ensure that the --profiling argument is set to false (Scored)

Number 2

Next task (2) is to check the ownership of directory /var/lib/etcd, so we first have a look:

➜ root@cluster2-controlplane1:~# ls -lh /var/lib | grep etcd
drwx------  3 root      root      4.0K Sep 11 20:08 etcd

ooks like user root and group root. Also possible to check using:

➜ root@cluster2-controlplane1:~# stat -c %U:%G /var/lib/etcd
root:root

But what has kube-bench to say about this?

➜ root@cluster2-controlplane1:~# kube-bench run --targets=master | grep "/var/lib/etcd" -B5

1.1.12 On the etcd server node, get the etcd data directory, passed as an argument --data-dir,
from the below command:
ps -ef | grep etcd
Run the below command (based on the etcd data directory found above).
For example, chown etcd:etcd /var/lib/etcd

To comply we run the following:

➜ root@cluster2-controlplane1:~# chown etcd:etcd /var/lib/etcd

➜ root@cluster2-controlplane1:~# ls -lh /var/lib | grep etcd
drwx------  3 etcd      etcd      4.0K Sep 11 20:08 etcd

This looks better. We run kube-bench again, and make sure test 1.1.12. is passing.

➜ root@cluster2-controlplane1:~# kube-bench run --targets=master | grep 1.1.12
[PASS] 1.1.12 Ensure that the etcd data directory ownership is set to etcd:etcd (Scored)

Done.

Number 3

To continue with number (3), we'll head to the worker node and ensure that the kubelet configuration file has the minimum necessary permissions as recommended:

➜ ssh cluster2-node1

➜ root@cluster2-node1:~# kube-bench run --targets=node
...
== Summary ==
13 checks PASS
10 checks FAIL
2 checks WARN
0 checks INFO

Also here some passes, fails and warnings. We check the permission level of the kubelet config file:

➜ root@cluster2-node1:~# stat -c %a /var/lib/kubelet/config.yaml
777

777 is highly permissive access level and not recommended by the kube-bench guidelines:

➜ root@cluster2-node1:~# kube-bench run --targets=node | grep /var/lib/kubelet/config.yaml -B2

4.1.9 Run the following command (using the config file location identified in the Audit step)
chmod 644 /var/lib/kubelet/config.yaml

We obey and set the recommended permissions:

➜ root@cluster2-node1:~# chmod 644 /var/lib/kubelet/config.yaml

➜ root@cluster2-node1:~# stat -c %a /var/lib/kubelet/config.yaml
644

And check if test 2.2.10 is passing:

➜ root@cluster2-node1:~# kube-bench run --targets=node | grep 4.1.9
[PASS] 2.2.10 Ensure that the kubelet configuration file has permissions set to 644 or more restrictive (Scored)

Number 4

Finally for number (4), let's check whether --client-ca-file argument for the kubelet is set properly according to kube-bench recommendations:

➜ root@cluster2-node1:~# kube-bench run --targets=node | grep client-ca-file
[PASS] 4.2.3 Ensure that the --client-ca-file argument is set as appropriate (Automated)

This looks passing with 4.2.3. The other ones are about the file that the parameter points to and can be ignored here.

To further investigate we run the following command to locate the kubelet config file, and open it:

➜ root@cluster2-node1:~# ps -ef | grep kubelet
root      5157     1  2 20:28 ?        00:03:22 /usr/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf --config=/var/lib/kubelet/config.yaml --network-plugin=cni --pod-infra-container-image=k8s.gcr.io/pause:3.2
root     19940 11901  0 22:38 pts/0    00:00:00 grep --color=auto kubelet

➜ root@croot@cluster2-node1:~# vim /var/lib/kubelet/config.yaml
# /var/lib/kubelet/config.yaml
apiVersion: kubelet.config.k8s.io/v1beta1
authentication:
  anonymous:
    enabled: false
  webhook:
    cacheTTL: 0s
    enabled: true
  x509:
    clientCAFile: /etc/kubernetes/pki/ca.crt
...

The clientCAFile points to the location of the certificate, which is correct.

第六题: Verify Platform Binaries

问题

Task weight: 2%

(can be solved in any kubectl context)

There are four Kubernetes server binaries located at /opt/course/6/binaries. You're provided with the following verified sha512 values for these:

  • kube-apiserver f417c0555bc0167355589dd1afe23be9bf909bf98312b1025f12015d1b58a1c62c9908c0067a7764fa35efdac7016a9efa8711a44425dd6692906a7c283f032c

  • kube-controller-manager 60100cc725e91fe1a949e1b2d0474237844b5862556e25c2c655a33boa8225855ec5ee22fa4927e6c46a60d43a7c4403a27268f96fbb726307d1608b44f38a60

  • kube-proxy 52f9d8ad045f8eee1d689619ef8ceef2d86d50c75a6a332653240d7ba5b2a114aca056d9e513984ade24358c9662714973c1960c62a5cb37dd375631c8a614c6

  • kubelet 4be40f2440619e990897cf956c32800dc96c2c983bf64519854a3309fa5aa21827991559f9c44595098e27e6f2ee4d64a3fdec6baba8a177881f20e3ec61e26c

Delete those binaries that don't match with the sha512 values above.

解答

We check the directory:

➜ cd /opt/course/6/binaries

➜ ls
kube-apiserver  kube-controller-manager  kube-proxy  kubelet

To generate the sha512 sum of a binary we do:

➜ sha512sum kube-apiserver 
f417c0555bc0167355589dd1afe23be9bf909bf98312b1025f12015d1b58a1c62c9908c0067a7764fa35efdac7016a9efa8711a44425dd6692906a7c283f032c  kube-apiserver

Looking good, next:

➜ sha512sum kube-controller-manager
60100cc725e91fe1a949e1b2d0474237844b5862556e25c2c655a33b0a8225855ec5ee22fa4927e6c46a60d43a7c4403a27268f96fbb726307d1608b44f38a60  kube-controller-manager

Okay, next:

➜ sha512sum kube-proxy
52f9d8ad045f8eee1d689619ef8ceef2d86d50c75a6a332653240d7ba5b2a114aca056d9e513984ade24358c9662714973c1960c62a5cb37dd375631c8a614c6  kube-proxy

Also good, and finally:

➜ sha512sum kubelet
7b720598e6a3483b45c537b57d759e3e82bc5c53b3274f681792f62e941019cde3d51a7f9b55158abf3810d506146bc0aa7cf97b36f27f341028a54431b335be  kubelet

Catch! Binary kubelet has a different hash!

But did we actually compare everything properly before? Let's have a closer look at kube-controller-manager again:

➜ sha512sum kube-controller-manager > compare

➜ vim compare 

Edit to only have the provided hash and the generated one in one line each:

# ./compare
60100cc725e91fe1a949e1b2d0474237844b5862556e25c2c655a33b0a8225855ec5ee22fa4927e6c46a60d43a7c4403a27268f96fbb726307d1608b44f38a60  
60100cc725e91fe1a949e1b2d0474237844b5862556e25c2c655a33boa8225855ec5ee22fa4927e6c46a60d43a7c4403a27268f96fbb726307d1608b44f38a60

Looks right at a first glance, but if we do:

➜ cat compare | uniq
60100cc725e91fe1a949e1b2d0474237844b5862556e25c2c655a33b0a8225855ec5ee22fa4927e6c46a60d43a7c4403a27268f96fbb726307d1608b44f38a60
60100cc725e91fe1a949e1b2d0474237844b5862556e25c2c655a33boa8225855ec5ee22fa4927e6c46a60d43a7c4403a27268f96fbb726307d1608b44f38a60

This shows they are different, by just one character actually.

To complete the task we do:

rm kubelet kube-controller-manager

第七题: Open Policy Agent

问题

Task weight: 6%

Use context: kubectl config use-context infra-prod

The Open Policy Agent and Gatekeeper have been installed to, among other things, enforce blacklisting of certain image registries. Alter the existing constraint and/or template to also blacklist images from very-bad-registry.com.

Test it by creating a single Pod using image very-bad-registry.com/image in Namespace default, it shouldn't work.

You can also verify your changes by looking at the existing Deployment untrusted in Namespace default, it uses an image from the new untrusted source. The OPA contraint should throw violation messages for this one.

解答

We look at existing OPA constraints, these are implemeted using CRDs by Gatekeeper:

➜ k get crd
NAME                                                 CREATED AT
blacklistimages.constraints.gatekeeper.sh            2020-09-14T19:29:31Z
configs.config.gatekeeper.sh                         2020-09-14T19:29:04Z
constraintpodstatuses.status.gatekeeper.sh           2020-09-14T19:29:05Z
constrainttemplatepodstatuses.status.gatekeeper.sh   2020-09-14T19:29:05Z
constrainttemplates.templates.gatekeeper.sh          2020-09-14T19:29:05Z
requiredlabels.constraints.gatekeeper.sh             2020-09-14T19:29:31Z

So we can do:

➜ k get constraint
NAME                                                           AGE
blacklistimages.constraints.gatekeeper.sh/pod-trusted-images   10m

NAME                                                                  AGE
requiredlabels.constraints.gatekeeper.sh/namespace-mandatory-labels   10m

and then look at the one that is probably about blacklisting images:

k edit blacklistimages pod-trusted-images
# kubectl edit blacklistimages pod-trusted-images
apiVersion: constraints.gatekeeper.sh/v1beta1
kind: BlacklistImages
metadata:
...
spec:
  match:
    kinds:
    - apiGroups:
      - ""
      kinds:
      - Pod

It looks like this constraint simply applies the template to all Pods, no arguments passed. So we edit the template:

k edit constrainttemplates blacklistimages
# kubectl edit constrainttemplates blacklistimages
apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
...
spec:
  crd:
    spec:
      names:
        kind: BlacklistImages
  targets:
  - rego: |
      package k8strustedimages

      images {
        image := input.review.object.spec.containers[_].image
        not startswith(image, "docker-fake.io/")
        not startswith(image, "google-gcr-fake.com/")
        not startswith(image, "very-bad-registry.com/") # ADD THIS LINE
      }

      violation[{"msg": msg}] {
        not images
        msg := "not trusted image!"
      }
    target: admission.k8s.gatekeeper.sh

We simply have to add another line. After editing we try to create a Pod of the bad image:

➜ k run opa-test --image=very-bad-registry.com/image
Error from server ([denied by pod-trusted-images] not trusted image!): admission webhook "validation.gatekeeper.sh" denied the request: [denied by pod-trusted-images] not trusted image!

Nice! After some time we can also see that Pods of the existing Deployment "untrusted" will be listed as violators:

➜ k describe blacklistimages pod-trusted-images
...
  Total Violations:  2
  Violations:
    Enforcement Action:  deny
    Kind:                Namespace
    Message:             you must provide labels: {"security-level"}
    Name:                sidecar-injector
    Enforcement Action:  deny
    Kind:                Pod
    Message:             not trusted image!
    Name:                untrusted-68c4944d48-tfsnb
    Namespace:           default
Events:                  <none>

Great, OPA fights bad registries !

第八题: Secure Kubernetes Dashboard

问题

Task weight: 3%

Use context: kubectl config use-context workload-prod

The Kubernetes Dashboard is installed in Namespace kubernetes-dashboard and is configured to:

  • Allow users to "skip login"
  • Allow insecure access (HTTP without authentication)
  • Allow basic authentication
  • Allow access from outside the cluster

You are asked to make it more secure by:

  • Deny users to "skip login"
  • Deny insecure access, enforce HTTPS (self signed certificates are ok for now)
  • Add the --auto-generate-certificates argument
  • Enforce authentication using a token (with possibility to use RBAC)
  • Allow only cluster internal access

解答

Head to https://github.com/kubernetes/dashboard/tree/master/docs to find documentation about the dashboard. This link is not on the allowed list of urls during the real exam. This means you should be provided will all information necessary in case of a task like this.

First we have a look in Namespace kubernetes-dashboard:

➜ k -n kubernetes-dashboard get pod,svc
NAME                                             READY   STATUS    RESTARTS   AGE
pod/dashboard-metrics-scraper-7b59f7d4df-fbpd9   1/1     Running   0          24m
pod/kubernetes-dashboard-6d8cd5dd84-w7wr2        1/1     Running   0          24m

NAME                                TYPE        ...   PORT(S)                        AGE
service/dashboard-metrics-scraper   ClusterIP   ...   8000/TCP                       24m
service/kubernetes-dashboard        NodePort    ...   9090:32520/TCP,443:31206/TCP   24m

We can see one running Pod and a NodePort Service exposing it. Let's try to connect to it via a NodePort, we can use IP of any Node:

(your port might be a different)

➜ k get node -o wide
NAME                     STATUS   ROLES    AGE   VERSION   INTERNAL-IP    ...
cluster1-controlplane1   Ready    master   37m   v1.28.2   192.168.100.11 ...
cluster1-node1           Ready    <none>   36m   v1.28.2   192.168.100.12 ...
cluster1-node2           Ready    <none>   34m   v1.28.2   192.168.100.13 ...

➜ curl http://192.168.100.11:32520
<!--
Copyright 2017 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

The dashboard is not secured because it allows unsecure HTTP access without authentication and is exposed externally. It's is loaded with a few parameter making it insecure, let's fix this.

First we create a backup in case we need to undo something:

k -n kubernetes-dashboard get deploy kubernetes-dashboard -oyaml > 8_deploy_kubernetes-dashboard.yaml

Then:

k -n kubernetes-dashboard edit deploy kubernetes-dashboard

The changes to make are :

template:
    spec:
      containers:
      - args:
        - --namespace=kubernetes-dashboard  
        - --authentication-mode=token        # change or delete, "token" is default
        - --auto-generate-certificates       # add
        #- --enable-skip-login=true          # delete or set to false
        #- --enable-insecure-login           # delete
        image: kubernetesui/dashboard:v2.0.3
        imagePullPolicy: Always
        name: kubernetes-dashboard

Next, we'll have to deal with the NodePort Service:

k -n kubernetes-dashboard get svc kubernetes-dashboard -o yaml > 8_svc_kubernetes-dashboard.yaml # backup

k -n kubernetes-dashboard edit svc kubernetes-dashboard

And make the following changes:

spec:
  clusterIP: 10.107.176.19
  externalTrafficPolicy: Cluster   # delete
  internalTrafficPolicy: Cluster
  ports:
  - name: http
    nodePort: 32513                # delete
    port: 9090
    protocol: TCP
    targetPort: 9090
  - name: https
    nodePort: 32441                # delete
    port: 443
    protocol: TCP
    targetPort: 8443
  selector:
    k8s-app: kubernetes-dashboard
  sessionAffinity: None
  type: ClusterIP                  # change or delete
status:
  loadBalancer: {}

Let's confirm the changes, we can do that even without having a browser:

➜ k run tmp --image=nginx:1.19.2 --restart=Never --rm -it -- bash
If you don't see a command prompt, try pressing enter.
root@tmp:/# curl http://kubernetes-dashboard.kubernetes-dashboard:9090
curl: (7) Failed to connect to kubernetes-dashboard.kubernetes-dashboard port 9090: Connection refused

➜ root@tmp:/# curl https://kubernetes-dashboard.kubernetes-dashboard
curl: (60) SSL certificate problem: self signed certificate
More details here: https://curl.haxx.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

➜ root@tmp:/# curl https://kubernetes-dashboard.kubernetes-dashboard -k
<!--
Copyright 2017 The Kubernetes Authors.

We see that insecure access is disabled and HTTPS works (using a self signed certificate for now). Let's also check the remote access:

(your port might be a different)

➜ curl http://192.168.100.11:32520
curl: (7) Failed to connect to 192.168.100.11 port 32520: Connection refused

➜ k -n kubernetes-dashboard get svc
NAME                        TYPE        CLUSTER-IP       ...   PORT(S)
dashboard-metrics-scraper   ClusterIP   10.111.171.247   ...   8000/TCP
kubernetes-dashboard        ClusterIP   10.100.118.128   ...   9090/TCP,443/TCP

Much better.

第九题: AppArmor Profile

Task weight: 3%

Use context: kubectl config use-context workload-prod

Some containers need to run more secure and restricted. There is an existing AppArmor profile located at/opt/course/9/profile for this.

  1. Install the AppArmor profile on Node cluster1-node1. Connect using ssh cluster1-node1.

  2. Add label security=apparmor to the Node

  3. Create a Deployment named apparmor in Namespace default with:

    • One replica of image nginx:1.19.2
    • NodeSelector for security=apparmor
    • Single container named c1 with the AppArmor profile enabled

The Pod might not run properly with the profile enabled. Write the logs of the Pod into /opt/course/9/logs so another team can work on getting the application running.

解答

参考链接: https://kubernetes.io/docs/tutorials/clusters/apparmor

Part 1

First we have a look at the provided profile:

vim /opt/course/9/profile
# /opt/course/9/profile 

#include <tunables/global>

profile very-secure flags=(attach_disconnected) {
  #include <abstractions/base>

  file,

  # Deny all file writes.
  deny /** w,
}

Very simple profile named very-secure which denies all file writes. Next we copy it onto the Node:

➜ scp /opt/course/9/profile cluster1-node1:~/
Warning: Permanently added the ECDSA host key for IP address '192.168.100.12' to the list of known hosts.
profile                                                                           100%  161   329.9KB/s   00:00

➜ ssh cluster1-node1

➜ root@cluster1-node1:~# ls
profile

And install it:

➜ root@cluster1-node1:~# apparmor_parser -q ./profile

Verify it has been installed:

➜ root@cluster1-node1:~# apparmor_status
apparmor module is loaded.
17 profiles are loaded.
17 profiles are in enforce mode.
   /sbin/dhclient
...
   man_filter
   man_groff
   very-secure
0 profiles are in complain mode.
56 processes have profiles defined.
56 processes are in enforce mode.
...
0 processes are in complain mode.
0 processes are unconfined but have a profile defined.

There we see among many others the very-secure one, which is the name of the profile specified in /opt/course/9/profile.

Part 2

We label the Node:

k label -h # show examples

k label node cluster1-node1 security=apparmor

Part 3

Now we can go ahead and create the Deployment which uses the profile.

k create deploy apparmor --image=nginx:1.19.2 $do > 9_deploy.yaml

vim 9_deploy.yaml
# 9_deploy.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: apparmor
  name: apparmor
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: apparmor
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: apparmor
      annotations:                                                                 # add
        container.apparmor.security.beta.kubernetes.io/c1: localhost/very-secure   # add
    spec:
      nodeSelector:                    # add
        security: apparmor             # add
      containers:
      - image: nginx:1.19.2
        name: c1                       # change
        resources: {}
k -f 9_deploy.yaml create

What the damage?

➜ k get pod -owide | grep apparmor
apparmor-85c65645dc-jbch8     0/1     CrashLoopBackOff  ...   cluster1-node1

➜ k logs apparmor-85c65645dc-w852p
/docker-entrypoint.sh: 13: /docker-entrypoint.sh: cannot create /dev/null: Permission denied
/docker-entrypoint.sh: No files found in /docker-entrypoint.d/, skipping configuration
2021/09/15 11:51:57 [emerg] 1#1: mkdir() "/var/cache/nginx/client_temp" failed (13: Permission denied)
nginx: [emerg] mkdir() "/var/cache/nginx/client_temp" failed (13: Permission denied)
```bash

This looks alright, the Pod is running on `cluster1-node1` because of the nodeSelector. The AppArmor profile simply denies all filesystem writes, but Nginx needs to write into some locations to run, hence the errors.

It looks like our profile is running but we can confirm this as well by inspecting the container:

```bash
➜ ssh cluster1-node1

➜ root@cluster1-node1:~# crictl pods | grep apparmor
be5c0aecee7c7       4 minutes ago       Ready               apparmor-85c65645dc-jbch8   ...

➜ root@cluster1-node1:~# crictl ps -a | grep be5c0aecee7c7
e4d91cbdf72fb    ...  Exited       c1           6            be5c0aecee7c7

➜ root@cluster1-node1:~# crictl inspect e4d91cbdf72fb | grep -i profile
          "apparmor_profile": "localhost/very-secure",
        "apparmorProfile": "very-secure",

First we find the Pod by it's name and get the pod-id. Next we use crictl ps -a to also show stopped containers. Then crictl inspect shows that the container is using our AppArmor profile. Notice to be fast between ps and inspect as K8s will restart the Pod periodically when in error state.

To complete the task we write the logs into the required location:

k logs apparmor-85c65645dc-jbch8 > /opt/course/9/logs

Fixing the errors is the job of another team, lucky us.

第十题: Container Runtime Sandbox gVisor

问题

Task weight: 4%

Use context: kubectl config use-context workload-prod

Team purple wants to run some of their workloads more secure. Worker node cluster1-node2 has container engine containerd already installed and it's configured to support the runsc/gvisor runtime.

Create a RuntimeClass named gvisor with handler runsc.

Create a Pod that uses the RuntimeClass. The Pod should be in Namespace team-purple, named gvisor-test and of image nginx:1.19.2. Make sure the Pod runs on cluster1-node2.

Write the dmesg output of the successfully started Pod into /opt/course/10/gvisor-test-dmesg.

解答

We check the nodes and we can see that all are using containerd:

➜ k get node -o wide
NAME                     STATUS   ROLES              ... CONTAINER-RUNTIME
cluster1-controlplane1   Ready    control-plane      ... containerd://1.5.2
cluster1-node1           Ready    <none>             ... containerd://1.5.2
cluster1-node2           Ready    <none>             ... containerd://1.5.2

But just one has containerd configured to work with runsc/gvisor runtime which is cluster1-node2.

(Optionally) we ssh into the worker node and check if containerd+runsc is configured:

➜ ssh cluster1-node2

➜ root@cluster1-node2:~# runsc --version
runsc version release-20201130.0
spec: 1.0.1-dev

➜ root@cluster1-node2:~# cat /etc/containerd/config.toml | grep runsc
  [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runsc]
    runtime_type = "io.containerd.runsc.v1"

Now we best head to the k8s docs for RuntimeClasses https://kubernetes.io/docs/concepts/containers/runtime-class, steal an example and create the gvisor one:

vim 10_rtc.yaml
# 10_rtc.yaml
apiVersion: node.k8s.io/v1
kind: RuntimeClass
metadata:
  name: gvisor
handler: runsc
k -f 10_rtc.yaml  create

And the required Pod:

k -n team-purple run gvisor-test --image=nginx:1.19.2 $do > 10_pod.yaml

vim 10_pod.yaml
# 10_pod.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: gvisor-test
  name: gvisor-test
  namespace: team-purple
spec:
  nodeName: cluster1-node2 # add
  runtimeClassName: gvisor   # add
  containers:
  - image: nginx:1.19.2
    name: gvisor-test
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
k -f 10_pod.yaml create

After creating the pod we should check if it's running and if it uses the gvisor sandbox:

➜ k -n team-purple get pod gvisor-test
NAME          READY   STATUS    RESTARTS   AGE
gvisor-test   1/1     Running   0          30s

➜ k -n team-purple exec gvisor-test -- dmesg
[    0.000000] Starting gVisor...
[    0.417740] Checking naughty and nice process list...
[    0.623721] Waiting for children...
[    0.902192] Gathering forks...
[    1.258087] Committing treasure map to memory...
[    1.653149] Generating random numbers by fair dice roll...
[    1.918386] Creating cloned children...
[    2.137450] Digging up root...
[    2.369841] Forking spaghetti code...
[    2.840216] Rewriting operating system in Javascript...
[    2.956226] Creating bureaucratic processes...
[    3.329981] Ready!

Looking good. And as required we finally write the dmesg output into the file:

k -n team-purple exec gvisor-test > /opt/course/10/gvisor-test-dmesg -- dmesg

第十一题: Secrets in ETCD

问题

Task weight: 7%

Use context: kubectl config use-context workload-prod

There is an existing Secret called database-access in Namespace team-green.

Read the complete Secret content directly from ETCD (using etcdctl) and store it into /opt/course/11/etcd-secret-content. Write the plain and decoded Secret's value of key "pass" into /opt/course/11/database-password.

解答

Let's try to get the Secret value directly from ETCD, which will work since it isn't encrypted.

First, we ssh into the master node where ETCD is running in this setup and check if etcdctl is installed and list it's options:

➜ ssh cluster1-controlplane1

➜ root@cluster1-controlplane1:~# etcdctl
NAME:
   etcdctl - A simple command line client for etcd.

WARNING:
   Environment variable ETCDCTL_API is not set; defaults to etcdctl v2.
   Set environment variable ETCDCTL_API=3 to use v3 API or ETCDCTL_API=2 to use v2 API.

USAGE:
   etcdctl [global options] command [command options] [arguments...]
...
   --cert-file value   identify HTTPS client using this SSL certificate file
   --key-file value    identify HTTPS client using this SSL key file
   --ca-file value     verify certificates of HTTPS-enabled servers using this CA bundle
...

Among others we see arguments to identify ourselves. The apiserver connects to ETCD, so we can run the following command to get the path of the necessary .crt and .key files:

cat /etc/kubernetes/manifests/kube-apiserver.yaml | grep etcd

The output is as follows :

    - --etcd-cafile=/etc/kubernetes/pki/etcd/ca.crt
    - --etcd-certfile=/etc/kubernetes/pki/apiserver-etcd-client.crt
    - --etcd-keyfile=/etc/kubernetes/pki/apiserver-etcd-client.key
    - --etcd-servers=https://127.0.0.1:2379 # optional since we're on same node

With this information we query ETCD for the secret value:

➜ root@cluster1-controlplane1:~# ETCDCTL_API=3 etcdctl \
--cert /etc/kubernetes/pki/apiserver-etcd-client.crt \
--key /etc/kubernetes/pki/apiserver-etcd-client.key \
--cacert /etc/kubernetes/pki/etcd/ca.crt get /registry/secrets/team-green/database-access

ETCD in Kubernetes stores data under /registry/{type}/{namespace}/{name}. This is how we came to look for /registry/secrets/team-green/database-access. There is also an example on a page in the k8s documentation which you could save as a bookmark to access fast during the exam.

The tasks requires us to store the output on our terminal. For this we can simply copy&paste the content into a new file on our terminal:

# /opt/course/11/etcd-secret-content
/registry/secrets/team-green/database-access
k8s


v1Secret

database-access
team-green"*$3e0acd78-709d-4f07-bdac-d5193d0f2aa32bB
0kubectl.kubernetes.io/last-applied-configuration{"apiVersion":"v1","data":{"pass":"Y29uZmlkZW50aWFs"},"kind":"Secret","metadata":{"annotations":{},"name":"database-access","namespace":"team-green"}}
z
kubectl-client-side-applyUpdatevFieldsV1:
{"f:data":{".":{},"f:pass":{}},"f:metadata":{"f:annotations":{".":{},"f:kubectl.kubernetes.io/last-applied-configuration":{}}},"f:type":{}}
pass
    confidentialOpaque"

We're also required to store the plain and "decrypted" database password. For this we can copy the base64-encoded value from the ETCD output and run on our terminal:

➜ echo Y29uZmlkZW50aWFs | base64 -d > /opt/course/11/database-password

➜ cat /opt/course/11/database-password
confidential

第十二题: Hack Secrets

问题

Task weight: 8%

Use context: kubectl config use-context restricted@infra-prod

You're asked to investigate a possible permission escape in Namespace restricted. The context authenticates as user restricted which has only limited permissions and shouldn't be able to read Secret values.

Try to find the password-key values of the Secrets secret1, secret2 and secret3 in Namespace restricted. Write the decoded plaintext values into files /opt/course/12/secret1, /opt/course/12/secret2 and /opt/course/12/secret3.

解答

First we should explore the boundaries, we can try:

➜ k -n restricted get role,rolebinding,clusterrole,clusterrolebinding
Error from server (Forbidden): roles.rbac.authorization.k8s.io is forbidden: User "restricted" cannot list resource "roles" in API group "rbac.authorization.k8s.io" in the namespace "restricted"
Error from server (Forbidden): rolebindings.rbac.authorization.k8s.io is forbidden: User "restricted" cannot list resource "rolebindings" in API group "rbac.authorization.k8s.io" in the namespace "restricted"
Error from server (Forbidden): clusterroles.rbac.authorization.k8s.io is forbidden: User "restricted" cannot list resource "clusterroles" in API group "rbac.authorization.k8s.io" at the cluster scope
Error from server (Forbidden): clusterrolebindings.rbac.authorization.k8s.io is forbidden: User "restricted" cannot list resource "clusterrolebindings" in API group "rbac.authorization.k8s.io" at the cluster scope

But no permissions to view RBAC resources. So we try the obvious:

➜ k -n restricted get secret
Error from server (Forbidden): secrets is forbidden: User "restricted" cannot list resource "secrets" in API group "" in the namespace "restricted"

➜ k -n restricted get secret -o yaml
apiVersion: v1
items: []
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""
Error from server (Forbidden): secrets is forbidden: User "restricted" cannot list resource "secrets" in API group "" in the namespace "restricted"

We're not allowed to get or list any Secrets. What can we see though?

➜ k -n restricted get all
NAME                    READY   STATUS    RESTARTS   AGE
pod1-fd5d64b9c-pcx6q    1/1     Running   0          37s
pod2-6494f7699b-4hks5   1/1     Running   0          37s
pod3-748b48594-24s76    1/1     Running   0          37s
Error from server (Forbidden): replicationcontrollers is forbidden: User "restricted" cannot list resource "replicationcontrollers" in API group "" in the namespace "restricted"
Error from server (Forbidden): services is forbidden: User "restricted" cannot list resource "services" in API group "" in the namespace "restricted"
...

There are some Pods, lets check these out regarding Secret access:

k -n restricted get pod -o yaml | grep -i secret

This output provides us with enough information to do:

➜ k -n restricted exec pod1-fd5d64b9c-pcx6q -- cat /etc/secret-volume/password
you-are

➜ echo you-are > /opt/course/12/secret1

And for the second Secret:

➜ k -n restricted exec pod2-6494f7699b-4hks5 -- env | grep PASS
PASSWORD=an-amazing

➜ echo an-amazing > /opt/course/12/secret2

None of the Pods seem to mount secret3 though. Can we create or edit existing Pods to mount secret3?

➜ k -n restricted run test --image=nginx
Error from server (Forbidden): pods is forbidden: User "restricted" cannot create resource "pods" in API group "" in the namespace "restricted"

➜ k -n restricted delete pod pod1
Error from server (Forbidden): pods "pod1" is forbidden: User "restricted" cannot delete resource "pods" in API group "" in the namespace "restricted"

Doesn't look like it.

But the Pods seem to be able to access the Secrets, we can try to use a Pod's ServiceAccount to access the third Secret. We can actually see (like using k -n restricted get pod -o yaml | grep automountServiceAccountToken) that only Pod pod3-* has the ServiceAccount token mounted:

➜ k -n restricted exec -it pod3-748b48594-24s76 -- sh

/ # mount | grep serviceaccount
tmpfs on /run/secrets/kubernetes.io/serviceaccount type tmpfs (ro,relatime)

/ # ls /run/secrets/kubernetes.io/serviceaccount
ca.crt     namespace  token

NOTE: You should have knowledge about ServiceAccounts and how they work with Pods like described in the docs

We can see all necessary information to contact the apiserver manually:

/ # curl https://kubernetes.default/api/v1/namespaces/restricted/secrets -H "Authorization: Bearer $(cat /run/secrets/kubernetes.io/serviceaccount/token)" -k
...
    {
      "metadata": {
        "name": "secret3",
        "namespace": "restricted",
...
          }
        ]
      },
      "data": {
        "password": "cEVuRXRSYVRpT24tdEVzVGVSCg=="
      },
      "type": "Opaque"
    }
...

Let's encode it and write it into the requested location:

➜ echo cEVuRXRSYVRpT24tdEVzVGVSCg== | base64 -d
pEnEtRaTiOn-tEsTeR

➜ echo cEVuRXRSYVRpT24tdEVzVGVSCg== | base64 -d > /opt/course/12/secret3

This will give us:

# /opt/course/12/secret1
you-are
# /opt/course/12/secret2
an-amazing
# /opt/course/12/secret3
pEnEtRaTiOn-tEsTeR

We hacked all Secrets! It can be tricky to get RBAC right and secure.

NOTE: One thing to consider is that giving the permission to "list" Secrets, will also allow the user to read the Secret values like using kubectl get secrets -o yaml even without the "get" permission set.

第十三题: Restrict access to Metadata Server

问题

Task weight: 7%

Use context: kubectl config use-context infra-prod

There is a metadata service available at http://192.168.100.21:32000 on which Nodes can reach sensitive data, like cloud credentials for initialisation. By default, all Pods in the cluster also have access to this endpoint. The DevSecOps team has asked you to restrict access to this metadata server.

In Namespace metadata-access:

  • Create a NetworkPolicy named metadata-deny which prevents egress to 192.168.100.21 for all Pods but still allows access to everything else
  • Create a NetworkPolicy named metadata-allow which allows Pods having label role: metadata-accessor to access endpoint 192.168.100.21

There are existing Pods in the target Namespace with which you can test your policies, but don't change their labels.

解答

There was a famous hack at Shopify which was based on revealed information via metadata for nodes.

Check the Pods in the Namespace metadata-access and their labels:

➜ k -n metadata-access get pods --show-labels
NAME                    ...   LABELS
pod1-7d67b4ff9-xrcd7    ...   app=pod1,pod-template-hash=7d67b4ff9
pod2-7b6fc66944-2hc7n   ...   app=pod2,pod-template-hash=7b6fc66944
pod3-7dc879bd59-hkgrr   ...   app=pod3,role=metadata-accessor,pod-template-hash=7dc879bd59

There are three Pods in the Namespace and one of them has the label role=metadata-accessor.

Check access to the metadata server from the Pods:

➜ k exec -it -n metadata-access pod1-7d67b4ff9-xrcd7 -- curl http://192.168.100.21:32000
metadata server

➜ k exec -it -n metadata-access pod2-7b6fc66944-2hc7n -- curl http://192.168.100.21:32000
metadata server

➜ k exec -it -n metadata-access pod3-7dc879bd59-hkgrr -- curl http://192.168.100.21:32000
metadata server

All three are able to access the metadata server.

To restrict the access, we create a NetworkPolicy to deny access to the specific IP.

vim 13_metadata-deny.yaml
# 13_metadata-deny.yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: metadata-deny
  namespace: metadata-access
spec:
  podSelector: {}
  policyTypes:
  - Egress
  egress:
  - to:
    - ipBlock:
        cidr: 0.0.0.0/0
        except:
        - 192.168.100.21/32
k -f 13_metadata-deny.yaml apply

NOTE: You should know about general default-deny K8s NetworkPolcies.

Verify that access to the metadata server has been blocked, but other endpoints are still accessible:

➜ k exec -it -n metadata-access pod1-7d67b4ff9-xrcd7 -- curl http://192.168.100.21:32000
curl: (28) Failed to connect to 192.168.100.21 port 32000: Operation timed out
command terminated with exit code 28

➜ kubectl exec -it -n metadata-access pod1-7d67b4ff9-xrcd7 -- curl -I https://kubernetes.io
HTTP/2 200
cache-control: public, max-age=0, must-revalidate
content-type: text/html; charset=UTF-8
date: Mon, 14 Sep 2020 15:39:39 GMT
etag: "b46e429397e5f1fecf48c10a533f5cd8-ssl"
strict-transport-security: max-age=31536000
age: 13
content-length: 22252
server: Netlify
x-nf-request-id: 1d94a1d1-6bac-4a98-b065-346f661f1db1-393998290

Similarly, verify for the other two Pods.

Now create another NetworkPolicy that allows access to the metadata server from Pods with label role=metadata-accessor.


vim 13_metadata-allow.yaml
# 13_metadata-allow.yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: metadata-allow
  namespace: metadata-access
spec:
  podSelector:
    matchLabels:
      role: metadata-accessor
  policyTypes:
  - Egress
  egress:
  - to:
    - ipBlock:
        cidr: 192.168.100.21/32
k -f 13_metadata-allow.yaml apply

Verify that required Pod has access to metadata endpoint and others do not:

➜ k -n metadata-access exec pod3-7dc879bd59-hkgrr -- curl http://192.168.100.21:32000
metadata server

➜ k -n metadata-access exec pod2-7b6fc66944-9ngzr  -- curl http://192.168.100.21:32000
^Ccommand terminated with exit code 130

It only works for the Pod having the label. With this we implemented the required security restrictions.

If a Pod doesn't have a matching NetworkPolicy then all traffic is allowed from and to it. Once a Pod has a matching NP then the contained rules are additive. This means that for Pods having label metadata-accessor the rules will be combined to:

# merged policies into one for pods with label metadata-accessor
spec:
  podSelector: {}
  policyTypes:
  - Egress
  egress:
  - to: # first rule
    - ipBlock: # condition 1
        cidr: 0.0.0.0/0
        except:
        - 192.168.100.21/32
  - to: # second rule
    - ipBlock: # condition 1
        cidr: 192.168.100.21/32

We can see that the merged NP contains two separate rules with one condition each. We could read it as:

Allow outgoing traffic if:
(destination is 0.0.0.0/0 but not 192.168.100.21/32) OR (destination is 192.168.100.21/32)

Hence it allows Pods with label metadata-accessor to access everything.

第十四题: Syscall Activity

问题

Task weight: 4%

Use context: kubectl config use-context workload-prod

There are Pods in Namespace team-yellow. A security investigation noticed that some processes running in these Pods are using the Syscall kill, which is forbidden by a Team Yellow internal policy.

Find the offending Pod(s) and remove these by reducing the replicas of the parent Deployment to 0.

解答

Syscalls are used by processes running in Userspace to communicate with the Linux Kernel. There are many available syscalls: https://man7.org/linux/man-pages/man2/syscalls.2.html. It makes sense to restrict these for container processes and Docker/Containerd already restrict some by default, like the reboot Syscall. Restricting even more is possible for example using Seccomp or AppArmor.

But for this task we should simply find out which binary process executes a specific Syscall. Processes in containers are simply run on the same Linux operating system, but isolated. That's why we first check on which nodes the Pods are running:

➜ k -n team-yellow get pod -owide
NAME                                 ...   NODE               NOMINATED NODE   ...
collector1-7585cc58cb-n5rtd   1/1    ...   cluster1-node1   <none>           ...
collector1-7585cc58cb-vdlp9   1/1    ...   cluster1-node1   <none>           ...
collector2-8556679d96-z7g7c   1/1    ...   cluster1-node1   <none>           ...
collector3-8b58fdc88-pjg24    1/1    ...   cluster1-node1   <none>           ...
collector3-8b58fdc88-s9ltc    1/1    ...   cluster1-node1   <none>           ...

All on cluster1-node1, hence we ssh into it and find the processes for the first Deployment collector1 .

➜ ssh cluster1-node1

➜ root@cluster1-node1:~# crictl pods --name collector1
POD ID              CREATED             STATE        NAME                          ...
21aacb8f4ca8d       17 minutes ago      Ready        collector1-7585cc58cb-vdlp9   ...
186631e40104d       17 minutes ago      Ready        collector1-7585cc58cb-n5rtd   ...

➜ root@cluster1-node1:~# crictl ps --pod 21aacb8f4ca8d
CONTAINER ID        IMAGE               CREATED          ...       POD ID
9ea02422f8660       5d867958e04e1       12 minutes ago   ...       21aacb8f4ca8d

➜ root@cluster1-node1:~# crictl inspect 9ea02422f8660 | grep args -A1
        "args": [
          "./collector1-process"
  • Using crictl pods we first searched for the Pods of Deployment `collector1, which has two replicas

  • We then took one pod-id to find it's containers using crictl ps

  • And finally we used crictl inspect to find the process name, which is collector1-process

We can find the process PIDs (two because there are two Pods):

➜ root@cluster1-node1:~# ps aux | grep collector1-process
root       35039  0.0  0.1 702208  1044 ?        Ssl  13:37   0:00 ./collector1-process
root       35059  0.0  0.1 702208  1044 ?        Ssl  13:37   0:00 ./collector1-process

Using the PIDs we can call strace to find Sycalls:

➜ root@cluster1-node1:~# strace -p 35039
strace: Process 35039 attached
futex(0x4d7e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
kill(666, SIGTERM)                      = -1 ESRCH (No such process)
epoll_pwait(3, [], 128, 999, NULL, 1)   = 0
kill(666, SIGTERM)                      = -1 ESRCH (No such process)
epoll_pwait(3, [], 128, 999, NULL, 1)   = 0
kill(666, SIGTERM)                      = -1 ESRCH (No such process)
epoll_pwait(3, ^Cstrace: Process 35039 detached
 <detached ...>
...

First try and already a catch! We see it uses the forbidden Syscall by calling kill(666, SIGTERM).

Next let's check the Deployment collector2 processes:

➜ root@cluster1-node1:~# ps aux | grep collector2-process
root       35375  0.0  0.0 702216   604 ?        Ssl  13:37   0:00 ./collector2-process

➜ root@cluster1-node1:~# strace -p 35375
strace: Process 35375 attached
futex(0x4d9e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
futex(0x4d9e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
futex(0x4d9e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
futex(0x4d9e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
...

Looks alright. What about collector3:

➜ root@cluster1-node1:~# ps aux | grep collector3-process
root       35155  0.0  0.1 702472  1040 ?        Ssl  13:37   0:00 ./collector3-process
root       35241  0.0  0.1 702472  1044 ?        Ssl  13:37   0:00 ./collector3-process

➜ root@cluster1-node1:~# strace -p 35155
strace: Process 35155 attached
futex(0x4d9e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
futex(0x4d9e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
futex(0x4d9e68, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
epoll_pwait(3, [], 128, 999, NULL, 1)   = 0
epoll_pwait(3, [], 128, 999, NULL, 1)   = 0
...

Also nothing about the forbidden Syscall. So we finalise the task:

k -n team-yellow scale deploy collector1 --replicas 0

And the world is a bit safer again.

第十五题: Configure TLS on Ingress

问题

Task weight: 4%

Use context: kubectl config use-context workload-prod

In Namespace team-pink there is an existing Nginx Ingress resources named secure which accepts two paths /app and /api which point to different ClusterIP Services.

From your main terminal you can connect to it using for example:

  • HTTP: curl -v http://secure-ingress.test:31080/app
  • HTTPS: curl -kv https://secure-ingress.test:31443/app

Right now it uses a default generated TLS certificate by the Nginx Ingress Controller.

You're asked to instead use the key and certificate provided at /opt/course/15/tls.key and /opt/course/15/tls.crt. As it's a self-signed certificate you need to use curl -k when connecting to it.

解答

Investigate

We can get the IP address of the Ingress and we see it's the same one to which secure-ingress.test is pointing to:

➜ k -n team-pink get ing secure 
NAME     CLASS    HOSTS                 ADDRESS          PORTS   AGE
secure   <none>   secure-ingress.test   192.168.100.12   80      7m11s

➜ ping secure-ingress.test
PING cluster1-node1 (192.168.100.12) 56(84) bytes of data.
64 bytes from cluster1-node1 (192.168.100.12): icmp_seq=1 ttl=64 time=0.316 ms

Now, let's try to access the paths /app and /api via HTTP:

➜ curl http://secure-ingress.test:31080/app
This is the backend APP!

➜ curl http://secure-ingress.test:31080/api
This is the API Server!

What about HTTPS?

➜ curl https://secure-ingress.test:31443/api
curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: https://curl.haxx.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

➜ curl -k https://secure-ingress.test:31443/api
This is the API Server!

HTTPS seems to be already working if we accept self-signed certificated using -k. But what kind of certificate is used by the server?

➜ curl -kv https://secure-ingress.test:31443/api
...
* Server certificate:
*  subject: O=Acme Co; CN=Kubernetes Ingress Controller Fake Certificate
*  start date: Sep 28 12:28:35 2020 GMT
*  expire date: Sep 28 12:28:35 2021 GMT
*  issuer: O=Acme Co; CN=Kubernetes Ingress Controller Fake Certificate
*  SSL certificate verify result: unable to get local issuer certificate (20), continuing anyway.
...

It seems to be "Kubernetes Ingress Controller Fake Certificate".

Implement own TLS certificate

First, let us generate a Secret using the provided key and certificate:

➜ cd /opt/course/15

➜ :/opt/course/15$ ls
tls.crt  tls.key

➜ :/opt/course/15$ k -n team-pink create secret tls tls-secret --key tls.key --cert tls.crt
secret/tls-secret created

Now, we configure the Ingress to make use of this Secret:

➜ k -n team-pink get ing secure -oyaml > 15_ing_bak.yaml

➜ k -n team-pink edit ing secure
# kubectl -n team-pink edit ing secure
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
...
  generation: 1
  name: secure
  namespace: team-pink
...
spec:
  tls:                            # add
    - hosts:                      # add
      - secure-ingress.test       # add
      secretName: tls-secret      # add
  rules:
  - host: secure-ingress.test
    http:
      paths:
      - backend:
          service:
            name: secure-app
            port: 80
        path: /app
        pathType: ImplementationSpecific
      - backend:
          service:
            name: secure-api
            port: 80
        path: /api
        pathType: ImplementationSpecific
...

After adding the changes we check the Ingress resource again:

➜ k -n team-pink get ing
NAME     CLASS    HOSTS                 ADDRESS          PORTS     AGE
secure   <none>   secure-ingress.test   192.168.100.12   80, 443   25m

It now actually lists port 443 for HTTPS. To verify:

➜ curl -k https://secure-ingress.test:31443/api
This is the API Server!

➜ curl -kv https://secure-ingress.test:31443/api
...
* Server certificate:
*  subject: CN=secure-ingress.test; O=secure-ingress.test
*  start date: Sep 25 18:22:10 2020 GMT
*  expire date: Sep 20 18:22:10 2040 GMT
*  issuer: CN=secure-ingress.test; O=secure-ingress.test
*  SSL certificate verify result: self signed certificate (18), continuing anyway.
...

We can see that the provided certificate is now being used by the Ingress for TLS termination.

第十六题: Docker Image Attack Surface

问题

Task weight: 7%

Use context: kubectl config use-context workload-prod

There is a Deployment image-verify in Namespace team-blue which runs image registry.killer.sh:5000/image-verify:v1. DevSecOps has asked you to improve this image by:

  • Changing the base image to alpine:3.12
  • Not installing curl
  • Updating nginx to use the version constraint >=1.18.0
  • Running the main process as user myuser

Do not add any new lines to the Dockerfile, just edit existing ones. The file is located at /opt/course/16/image/Dockerfile.

Tag your version as v2. You can build, tag and push using:

cd /opt/course/16/image
podman build -t registry.killer.sh:5000/image-verify:v2 .
podman run registry.killer.sh:5000/image-verify:v2 # to test your changes
podman push registry.killer.sh:5000/image-verify:v2
Make the Deployment use your updated image tag v2.

Make the Deployment use your updated image tag v2.

解答

We should have a look at the Docker Image at first:

cd /opt/course/16/image

cp Dockerfile Dockerfile.bak

vim Dockerfile
# /opt/course/16/image/Dockerfile
FROM alpine:3.4
RUN apk update && apk add vim curl nginx=1.10.3-r0
RUN addgroup -S myuser && adduser -S myuser -G myuser
COPY ./run.sh run.sh
RUN ["chmod", "+x", "./run.sh"]
USER root
ENTRYPOINT ["/bin/sh", "./run.sh"]

Very simple Dockerfile which seems to execute a script run.sh :

# /opt/course/16/image/run.sh
while true; do date; id; echo; sleep 1; done

So it only outputs current date and credential information in a loop. We can see that output in the existing Deployment image-verify:

➜ k -n team-blue logs -f -l id=image-verify
Fri Sep 25 20:59:12 UTC 2020
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy),20(dialout),26(tape),27(video)

We see it's running as root.

Next we update the Dockerfile according to the requirements:

# /opt/course/16/image/Dockerfile

# change
FROM alpine:3.12

# change
RUN apk update && apk add vim nginx>=1.18.0

RUN addgroup -S myuser && adduser -S myuser -G myuser
COPY ./run.sh run.sh
RUN ["chmod", "+x", "./run.sh"]

# change
USER myuser

ENTRYPOINT ["/bin/sh", "./run.sh"]

Then we build the new image:

➜ :/opt/course/16/image$ podman build -t registry.killer.sh:5000/image-verify:v2 .
...
STEP 7/7: ENTRYPOINT ["/bin/sh", "./run.sh"]
COMMIT registry.killer.sh:5000/image-verify:v2
--> ceb8989101b
Successfully tagged registry.killer.sh:5000/image-verify:v2
ceb8989101bccd9f6b9c3b4c6c75f6c3561f19a5b784edd1f1a36fa0fb34a9df

We can then test our changes by running the container locally:

➜ :/opt/course/16/image$ podman run registry.killer.sh:5000/image-verify:v2 
Thu Sep 16 06:01:47 UTC 2021
uid=101(myuser) gid=102(myuser) groups=102(myuser)

Thu Sep 16 06:01:48 UTC 2021
uid=101(myuser) gid=102(myuser) groups=102(myuser)

Thu Sep 16 06:01:49 UTC 2021
uid=101(myuser) gid=102(myuser) groups=102(myuser)

Looking good, so we push:

➜ :/opt/course/16/image$ podman push registry.killer.sh:5000/image-verify:v2
Getting image source signatures
Copying blob cd0853834d88 done  
Copying blob 5298d0709c3e skipped: already exists  
Copying blob e6688e911f15 done  
Copying blob dbc406096645 skipped: already exists  
Copying blob 98895ed393d9 done  
Copying config ceb8989101 done  
Writing manifest to image destination
Storing signatures

And we update the Deployment to use the new image:

k -n team-blue edit deploy image-verify
# kubectl -n team-blue edit deploy image-verify
apiVersion: apps/v1
kind: Deployment
metadata:
...
spec:
...
  template:
...
    spec:
      containers:
      - image: registry.killer.sh:5000/image-verify:v2 # change

And afterwards we can verify our changes by looking at the Pod logs:

➜ k -n team-blue logs -f -l id=image-verify
Fri Sep 25 21:06:55 UTC 2020
uid=101(myuser) gid=102(myuser) groups=102(myuser)

Also to verify our changes even further:

➜ k -n team-blue exec image-verify-55fbcd4c9b-x2flc -- curl
OCI runtime exec failed: exec failed: container_linux.go:349: starting container process caused "exec: \"curl\": executable file not found in $PATH": unknown
command terminated with exit code 126

➜ k -n team-blue exec image-verify-55fbcd4c9b-x2flc -- nginx -v
nginx version: nginx/1.18.0

Another task solved.

第十七题: Audit Log Policy

问题

Task weight: 7%

Use context: kubectl config use-context infra-prod

Audit Logging has been enabled in the cluster with an Audit Policy located at /etc/kubernetes/audit/policy.yaml on cluster2-controlplane1.

Change the configuration so that only one backup of the logs is stored.

Alter the Policy in a way that it only stores logs:

  • From Secret resources, level Metadata
  • From "system:nodes" userGroups, level RequestResponse

After you altered the Policy make sure to empty the log file so it only contains entries according to your changes, like using truncate -s 0 /etc/kubernetes/audit/logs/audit.log.

NOTE: You can use jq to render json more readable. cat data.json | jq

解答

First we check the apiserver configuration and change as requested:

➜ ssh cluster2-controlplane1

➜ root@cluster2-controlplane1:~# cp /etc/kubernetes/manifests/kube-apiserver.yaml ~/17_kube-apiserver.yaml # backup

➜ root@cluster2-controlplane1:~# vim /etc/kubernetes/manifests/kube-apiserver.yaml 
# /etc/kubernetes/manifests/kube-apiserver.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    component: kube-apiserver
    tier: control-plane
  name: kube-apiserver
  namespace: kube-system
spec:
  containers:
  - command:
    - kube-apiserver
    - --audit-policy-file=/etc/kubernetes/audit/policy.yaml
    - --audit-log-path=/etc/kubernetes/audit/logs/audit.log
    - --audit-log-maxsize=5
    - --audit-log-maxbackup=1                                    # CHANGE
    - --advertise-address=192.168.100.21
    - --allow-privileged=true
...

NOTE: You should know how to enable Audit Logging completely yourself as described in the docs. Feel free to try this in another cluster in this environment.

Now we look at the existing Policy:

➜ root@cluster2-controlplane1:~# vim /etc/kubernetes/audit/policy.yaml
# /etc/kubernetes/audit/policy.yaml
apiVersion: audit.k8s.io/v1
kind: Policy
rules:
- level: Metadata

We can see that this simple Policy logs everything on Metadata level. So we change it to the requirements:

# /etc/kubernetes/audit/policy.yaml
apiVersion: audit.k8s.io/v1
kind: Policy
rules:

# log Secret resources audits, level Metadata
- level: Metadata
  resources:
  - group: ""
    resources: ["secrets"]

# log node related audits, level RequestResponse
- level: RequestResponse
  userGroups: ["system:nodes"]

# for everything else don't log anything
- level: None

After saving the changes we have to restart the apiserver:

➜ root@cluster2-controlplane1:~# cd /etc/kubernetes/manifests/

➜ root@cluster2-controlplane1:/etc/kubernetes/manifests# mv kube-apiserver.yaml ..

➜ root@cluster2-controlplane1:/etc/kubernetes/manifests# watch crictl ps # wait for apiserver gone

➜ root@cluster2-controlplane1:/etc/kubernetes/manifests# truncate -s 0 /etc/kubernetes/audit/logs/audit.log

➜ root@cluster2-controlplane1:/etc/kubernetes/manifests# mv ../kube-apiserver.yaml .

Once the apiserver is running again we can check the new logs and scroll through some entries:

cat audit.log | tail | jq
{
  "kind": "Event",
  "apiVersion": "audit.k8s.io/v1",
  "level": "Metadata",
  "auditID": "e598dc9e-fc8b-4213-aee3-0719499ab1bd",
  "stage": "RequestReceived",
  "requestURI": "...",
  "verb": "watch",
  "user": {
    "username": "system:serviceaccount:gatekeeper-system:gatekeeper-admin",
    "uid": "79870838-75a8-479b-ad42-4b7b75bd17a3",
    "groups": [
      "system:serviceaccounts",
      "system:serviceaccounts:gatekeeper-system",
      "system:authenticated"
    ]
  },
  "sourceIPs": [
    "192.168.102.21"
  ],
  "userAgent": "manager/v0.0.0 (linux/amd64) kubernetes/$Format",
  "objectRef": {
    "resource": "secrets",
    "apiVersion": "v1"
  },
  "requestReceivedTimestamp": "2020-09-27T20:01:36.238911Z",
  "stageTimestamp": "2020-09-27T20:01:36.238911Z",
  "annotations": {
    "authentication.k8s.io/legacy-token": "..."
  }
}

Above we logged a watch action by OPA Gatekeeper for Secrets, level Metadata.

{
  "kind": "Event",
  "apiVersion": "audit.k8s.io/v1",
  "level": "RequestResponse",
  "auditID": "c90e53ed-b0cf-4cc4-889a-f1204dd39267",
  "stage": "ResponseComplete",
  "requestURI": "...",
  "verb": "list",
  "user": {
    "username": "system:node:cluster2-controlplane1",
    "groups": [
      "system:nodes",
      "system:authenticated"
    ]
  },
  "sourceIPs": [
    "192.168.100.21"
  ],
  "userAgent": "kubelet/v1.19.1 (linux/amd64) kubernetes/206bcad",
  "objectRef": {
    "resource": "configmaps",
    "namespace": "kube-system",
    "name": "kube-proxy",
    "apiVersion": "v1"
  },
  "responseStatus": {
    "metadata": {},
    "code": 200
  },
  "responseObject": {
    "kind": "ConfigMapList",
    "apiVersion": "v1",
    "metadata": {
      "selfLink": "/api/v1/namespaces/kube-system/configmaps",
      "resourceVersion": "83409"
    },
    "items": [
      {
        "metadata": {
          "name": "kube-proxy",
          "namespace": "kube-system",
          "selfLink": "/api/v1/namespaces/kube-system/configmaps/kube-proxy",
          "uid": "0f1c3950-430a-4543-83e4-3f9c87a478b8",
          "resourceVersion": "232",
          "creationTimestamp": "2020-09-26T20:59:50Z",
          "labels": {
            "app": "kube-proxy"
          },
          "annotations": {
            "kubeadm.kubernetes.io/component-config.hash": "..."
          },
          "managedFields": [
            {
...
            }
          ]
        },
...
      }
    ]
  },
  "requestReceivedTimestamp": "2020-09-27T20:01:36.223781Z",
  "stageTimestamp": "2020-09-27T20:01:36.225470Z",
  "annotations": {
    "authorization.k8s.io/decision": "allow",
    "authorization.k8s.io/reason": ""
  }
}

And in the one above we logged a list action by system:nodes for a ConfigMaps, level RequestResponse.

Because all JSON entries are written in a single line in the file we could also run some simple verifications on our Policy:


# shows Secret entries
cat audit.log | grep '"resource":"secrets"' | wc -l

# confirms Secret entries are only of level Metadata
cat audit.log | grep '"resource":"secrets"' | grep -v '"level":"Metadata"' | wc -l

# shows RequestResponse level entries
cat audit.log | grep -v '"level":"RequestResponse"' | wc -l

# shows RequestResponse level entries are only for system:nodes
cat audit.log | grep '"level":"RequestResponse"' | grep -v "system:nodes" | wc -l

Looks like our job is done.

第十八题: Investigate Break-in via Audit Log

问题

Task weight: 4%

Use context: kubectl config use-context infra-prod

Namespace security contains five Secrets of type Opaque which can be considered highly confidential. The latest Incident-Prevention-Investigation revealed that ServiceAccount p.auster had too broad access to the cluster for some time. This SA should've never had access to any Secrets in that Namespace.

Find out which Secrets in Namespace security this SA did access by looking at the Audit Logs under /opt/course/18/audit.log.

Change the password to any new string of only those Secrets that were accessed by this SA.

NOTE: You can use jq to render json more readable. cat data.json | jq

解答

First we look at the Secrets this is about:

➜ k -n security get secret | grep Opaque
kubeadmin-token       Opaque                                1      37m
mysql-admin           Opaque                                1      37m
postgres001           Opaque                                1      37m
postgres002           Opaque                                1      37m
vault-token           Opaque                                1      37m

Next we investigate the Audit Log file:

➜ cd /opt/course/18

➜ :/opt/course/18$ ls -lh
total 7.1M
-rw-r--r-- 1 k8s k8s 7.5M Sep 24 21:31 audit.log

➜ :/opt/course/18$ cat audit.log | wc -l
4451

Audit Logs can be huge and it's common to limit the amount by creating an Audit Policy and to transfer the data in systems like Elasticsearch. In this case we have a simple JSON export, but it already contains 4451 lines.

We should try to filter the file down to relevant information:

➜ :/opt/course/18$ cat audit.log | grep "p.auster" | wc -l
28

Not too bad, only 28 logs for ServiceAccount p.auster.

➜ :/opt/course/18$ cat audit.log | grep "p.auster" | grep Secret | wc -l
2

And only 2 logs related to Secrets...

➜ :/opt/course/18$ cat audit.log | grep "p.auster" | grep Secret | grep list | wc -l
0

➜ :/opt/course/18$ cat audit.log | grep "p.auster" | grep Secret | grep get | wc -l
2

No list actions, which is good, but 2 get actions, so we check these out:

cat audit.log | grep "p.auster" | grep Secret | grep get | jq
{
  "kind": "Event",
  "apiVersion": "audit.k8s.io/v1",
  "level": "RequestResponse",
  "auditID": "74fd9e03-abea-4df1-b3d0-9cfeff9ad97a",
  "stage": "ResponseComplete",
  "requestURI": "/api/v1/namespaces/security/secrets/vault-token",
  "verb": "get",
  "user": {
    "username": "system:serviceaccount:security:p.auster",
    "uid": "29ecb107-c0e8-4f2d-816a-b16f4391999c",
    "groups": [
      "system:serviceaccounts",
      "system:serviceaccounts:security",
      "system:authenticated"
    ]
  },
...
  "userAgent": "curl/7.64.0",
  "objectRef": {
    "resource": "secrets",
    "namespace": "security",
    "name": "vault-token",
    "apiVersion": "v1"
  },
 ...
}
{
  "kind": "Event",
  "apiVersion": "audit.k8s.io/v1",
  "level": "RequestResponse",
  "auditID": "aed6caf9-5af0-4872-8f09-ad55974bb5e0",
  "stage": "ResponseComplete",
  "requestURI": "/api/v1/namespaces/security/secrets/mysql-admin",
  "verb": "get",
  "user": {
    "username": "system:serviceaccount:security:p.auster",
    "uid": "29ecb107-c0e8-4f2d-816a-b16f4391999c",
    "groups": [
      "system:serviceaccounts",
      "system:serviceaccounts:security",
      "system:authenticated"
    ]
  },
...
  "userAgent": "curl/7.64.0",
  "objectRef": {
    "resource": "secrets",
    "namespace": "security",
    "name": "mysql-admin",
    "apiVersion": "v1"
  },
...
}

There we see that Secrets vault-token and mysql-admin were accessed by p.auster. Hence we change the passwords for those.

➜ echo new-vault-pass | base64
bmV3LXZhdWx0LXBhc3MK

➜ k -n security edit secret vault-token

➜ echo new-mysql-pass | base64
bmV3LW15c3FsLXBhc3MK

➜ k -n security edit secret mysql-admin
```bash

Audit Logs ftw.

By running cat audit.log | grep "p.auster" | grep Secret | grep password we can see that passwords are stored in the Audit Logs, because they store the complete content of Secrets. It's never a good idea to reveal passwords in logs. In this case it would probably be sufficient to only store Metadata level information of Secrets which can be controlled via a Audit Policy.

第十九题: Immutable Root FileSystem

问题:

Task weight: 2%

Use context: kubectl config use-context workload-prod

The Deployment immutable-deployment in Namespace team-purple should run immutable, it's created from file /opt/course/19/immutable-deployment.yaml. Even after a successful break-in, it shouldn't be possible for an attacker to modify the filesystem of the running container.

Modify the Deployment in a way that no processes inside the container can modify the local filesystem, only /tmp directory should be writeable. Don't modify the Docker image.

Save the updated YAML under /opt/course/19/immutable-deployment-new.yaml and update the running Deployment.

解答

Processes in containers can write to the local filesystem by default. This increases the attack surface when a non-malicious process gets hijacked. Preventing applications to write to disk or only allowing to certain directories can mitigate the risk. If there is for example a bug in Nginx which allows an attacker to override any file inside the container, then this only works if the Nginx process itself can write to the filesystem in the first place.

Making the root filesystem readonly can be done in the Docker image itself or in a Pod declaration.

Let us first check the Deployment immutable-deployment in Namespaceteam-purple:

➜ k -n team-purple edit deploy -o yaml
# kubectl -n team-purple edit deploy -o yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  namespace: team-purple
  name: immutable-deployment
  labels:
    app: immutable-deployment
  ...
spec:
  replicas: 1
  selector:
    matchLabels:
      app: immutable-deployment
  template:
    metadata:
      labels:
        app: immutable-deployment
    spec:
      containers:
      - image: busybox:1.32.0
        command: ['sh', '-c', 'tail -f /dev/null']
        imagePullPolicy: IfNotPresent
        name: busybox
      restartPolicy: Always
...

The container has write access to the Root File System, as there are no restrictions defined for the Pods or containers by an existing SecurityContext. And based on the task we're not allowed to alter the Docker image.

So we modify the YAML manifest to include the required changes:

cp /opt/course/19/immutable-deployment.yaml /opt/course/19/immutable-deployment-new.yaml

vim /opt/course/19/immutable-deployment-new.yaml
# /opt/course/19/immutable-deployment-new.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  namespace: team-purple
  name: immutable-deployment
  labels:
    app: immutable-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: immutable-deployment
  template:
    metadata:
      labels:
        app: immutable-deployment
    spec:
      containers:
      - image: busybox:1.32.0
        command: ['sh', '-c', 'tail -f /dev/null']
        imagePullPolicy: IfNotPresent
        name: busybox
        securityContext:                  # add
          readOnlyRootFilesystem: true    # add
        volumeMounts:                     # add
        - mountPath: /tmp                 # add
          name: temp-vol                  # add
      volumes:                            # add
      - name: temp-vol                    # add
        emptyDir: {}                      # add
      restartPolicy: Always

SecurityContexts can be set on Pod or container level, here the latter was asked. Enforcing readOnlyRootFilesystem: true will render the root filesystem readonly. We can then allow some directories to be writable by using an emptyDir volume.

Once the changes are made, let us update the Deployment:

➜ k delete -f /opt/course/19/immutable-deployment-new.yaml
deployment.apps "immutable-deployment" deleted

➜ k create -f /opt/course/19/immutable-deployment-new.yaml
deployment.apps/immutable-deployment created

We can verify if the required changes are propagated:

➜ k -n team-purple exec immutable-deployment-5b7ff8d464-j2nrj -- touch /abc.txt
touch: /abc.txt: Read-only file system
command terminated with exit code 1

➜ k -n team-purple exec immutable-deployment-5b7ff8d464-j2nrj -- touch /var/abc.txt
touch: /var/abc.txt: Read-only file system
command terminated with exit code 1

➜ k -n team-purple exec immutable-deployment-5b7ff8d464-j2nrj -- touch /etc/abc.txt
touch: /etc/abc.txt: Read-only file system
command terminated with exit code 1

➜ k -n team-purple exec immutable-deployment-5b7ff8d464-j2nrj -- touch /tmp/abc.txt

➜ k -n team-purple exec immutable-deployment-5b7ff8d464-j2nrj -- ls /tmp
abc.txt

The Deployment has been updated so that the container's file system is read-only, and the updated YAML has been placed under the required location. Sweet!

第二十题: Update Kubernetes

问题

Task weight: 8%

Use context: kubectl config use-context workload-stage

The cluster is running Kubernetes 1.27.6, update it to 1.28.2.

Use apt package manager and kubeadm for this.

Use ssh cluster3-controlplane1 and ssh cluster3-node1 to connect to the instances.

解决

过程总结:

  1. 先升级Master节点

    • 驱逐pod
    • 升级kubeadm
    • 执行升级计算和应用升级
    • 升级kubelet和kubectl
    • 恢复驱逐pod
  2. 在升级Node节点 (所有node节点)

    • 驱逐pod
    • 升级kubeadm
    • 执行升级节点
    • 升级kubelet和kubectl
    • 恢复驱逐pod

Let's have a look at the current versions:

➜ k get node
cluster3-controlplane1   Ready    control-plane   96m   v1.27.6
cluster3-node1           Ready    <none>          91m   v1.27.6

Control Plane Master Components

First we should update the control plane components running on the master node, so we drain it:

➜ k drain cluster3-controlplane1 --ignore-daemonsets

Next we ssh into it and check versions:

➜ ssh cluster3-controlplane1

➜ root@cluster3-controlplane1:~# kubelet --version
Kubernetes v1.27.6

➜ root@cluster3-controlplane1:~# kubeadm version
kubeadm version: &version.Info{Major:"1", Minor:"28", GitVersion:"v1.28.2", GitCommit:"89a4ea3e1e4ddd7f7572286090359983e0387b2f", GitTreeState:"clean", BuildDate:"2023-09-13T09:34:32Z", GoVersion:"go1.20.8", Compiler:"gc", Platform:"linux/amd64"}

We see above that kubeadm is already installed in the required version. Else we would need to install it:

# not necessary because here kubeadm is already installed in correct version
apt-mark unhold kubeadm
apt-mark hold kubectl kubelet
apt install kubeadm=1.28.2-00
apt-mark hold kubeadm

Check what kubeadm has available as an upgrade plan:

➜ root@cluster3-controlplane1:~# kubeadm upgrade plan
[upgrade/config] Making sure the configuration is correct:
[upgrade/config] Reading configuration from the cluster...
[upgrade/config] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[preflight] Running pre-flight checks.
[upgrade] Running cluster health checks
[upgrade] Fetching available versions to upgrade to
[upgrade/versions] Cluster version: v1.27.6
[upgrade/versions] kubeadm version: v1.28.2
[upgrade/versions] Target version: v1.28.2
[upgrade/versions] Latest version in the v1.27 series: v1.27.6

Components that must be upgraded manually after you have upgraded the control plane with 'kubeadm upgrade apply':
COMPONENT   CURRENT       TARGET
kubelet     2 x v1.27.6   v1.28.2

Upgrade to the latest stable version:

COMPONENT                 CURRENT   TARGET
kube-apiserver            v1.27.6   v1.28.2
kube-controller-manager   v1.27.6   v1.28.2
kube-scheduler            v1.27.6   v1.28.2
kube-proxy                v1.27.6   v1.28.2
CoreDNS                   v1.10.1   v1.10.1
etcd                      3.5.7-0   3.5.9-0

You can now apply the upgrade by executing the following command:

        kubeadm upgrade apply v1.28.2

_____________________________________________________________________


The table below shows the current state of component configs as understood by this version of kubeadm.
Configs that have a "yes" mark in the "MANUAL UPGRADE REQUIRED" column require manual config upgrade or
resetting to kubeadm defaults before a successful upgrade can be performed. The version to manually
upgrade to is denoted in the "PREFERRED VERSION" column.

API GROUP                 CURRENT VERSION   PREFERRED VERSION   MANUAL UPGRADE REQUIRED
kubeproxy.config.k8s.io   v1alpha1          v1alpha1            no
kubelet.config.k8s.io     v1beta1           v1beta1             no
_____________________________________________________________________

And we apply to the required version:

➜ root@cluster3-controlplane1:~# kubeadm upgrade apply v1.28.2
[upgrade/config] Making sure the configuration is correct:
[upgrade/config] Reading configuration from the cluster...
[upgrade/config] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[preflight] Running pre-flight checks.
[upgrade] Running cluster health checks
[upgrade/version] You have chosen to change the cluster version to "v1.28.2"
[upgrade/versions] Cluster version: v1.27.6
[upgrade/versions] kubeadm version: v1.28.2
[upgrade] Are you sure you want to proceed? [y/N]: y
[upgrade/prepull] Pulling images required for setting up a Kubernetes cluster
...
[bootstrap-token] Configured RBAC rules to allow certificate rotation for all node client certificates in the cluster
[addons] Applied essential addon: CoreDNS
[addons] Applied essential addon: kube-proxy

[upgrade/successful] SUCCESS! Your cluster was upgraded to "v1.28.2". Enjoy!

[upgrade/kubelet] Now that your control plane is upgraded, please proceed with upgrading your kubelets if you haven't already done so.

Next we can check if our required version was installed correctly:

➜ root@cluster3-controlplane1:~# kubeadm upgrade plan
[upgrade/config] Making sure the configuration is correct:
[upgrade/config] Reading configuration from the cluster...
[upgrade/config] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[preflight] Running pre-flight checks.
[upgrade] Running cluster health checks
[upgrade] Fetching available versions to upgrade to
[upgrade/versions] Cluster version: v1.28.2
[upgrade/versions] kubeadm version: v1.28.2
[upgrade/versions] Target version: v1.28.2
[upgrade/versions] Latest version in the v1.28 series: v1.28.2

Control Plane kubelet and kubectl

Now we have to upgrade kubelet and kubectl:

➜ root@cluster3-controlplane1:~# apt update
Hit:1 http://ppa.launchpad.net/rmescandon/yq/ubuntu focal InRelease
Hit:3 http://us.archive.ubuntu.com/ubuntu bionic InRelease                 
Hit:2 https://packages.cloud.google.com/apt kubernetes-xenial InRelease
Reading package lists... Done                               
Building dependency tree       
Reading state information... Done
2 packages can be upgraded. Run 'apt list --upgradable' to see them.

➜ root@cluster3-controlplane1:~# apt-mark unhold kubelet kubectl
kubelet was already not hold.
kubectl was already not hold.

➜ root@cluster3-controlplane1:~# apt install kubelet=1.28.2-00 kubectl=1.28.2-00
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
  kubectl kubelet
2 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 29.8 MB of archives.
After this operation, 5,194 kB of additional disk space will be used.
Get:1 https://packages.cloud.google.com/apt kubernetes-xenial/main amd64 kubectl amd64 1.28.2-00 [10.3 MB]
Get:2 https://packages.cloud.google.com/apt kubernetes-xenial/main amd64 kubelet amd64 1.28.2-00 [19.5 MB]
Fetched 29.8 MB in 2s (17.3 MB/s)   
(Reading database ... 112527 files and directories currently installed.)
Preparing to unpack .../kubectl_1.28.2-00_amd64.deb ...
Unpacking kubectl (1.28.2-00) over (1.27.6-00) ...
Preparing to unpack .../kubelet_1.28.2-00_amd64.deb ...
Unpacking kubelet (1.28.2-00) over (1.27.6-00) ...
Setting up kubectl (1.28.2-00) ...
Setting up kubelet (1.28.2-00) ...

➜ root@cluster3-controlplane1:~# apt-mark hold kubelet kubectl
kubelet set on hold.
kubectl set on hold.

➜ root@cluster3-controlplane1:~# service kubelet restart

➜ root@cluster3-controlplane1:~# service kubelet status
● kubelet.service - kubelet: The Kubernetes Node Agent
     Loaded: loaded (/lib/systemd/system/kubelet.service; enabled; vendor preset: enabled)
    Drop-In: /etc/systemd/system/kubelet.service.d
             └─10-kubeadm.conf
     Active: active (running) since Tue 2023-09-26 12:52:25 UTC; 3s ago
       Docs: https://kubernetes.io/docs/home/
   Main PID: 34030 (kubelet)
      Tasks: 11 (limit: 1066)
     Memory: 34.4M
     CGroup: /system.slice/kubelet.service
...

➜ root@cluster3-controlplane1:~# kubectl get node
NAME                     STATUS                     ROLES           AGE    VERSION
cluster3-controlplane1   Ready,SchedulingDisabled   control-plane   150m   v1.28.2
cluster3-node1           Ready                      <none>          143m   v1.27.6

Done, and uncordon:

➜ k uncordon cluster3-controlplane1
node/cluster3-controlplane1 uncordoned

Data Plane

➜ k get node
NAME                     STATUS   ROLES           AGE    VERSION
cluster3-controlplane1   Ready    control-plane   150m   v1.28.2
cluster3-node1           Ready    <none>          143m   v1.27.6

Our data plane consist of one single worker node, so let's update it. First thing is we should drain it:

k drain cluster3-node1 --ignore-daemonsets

Next we ssh into it and upgrade kubeadm to the wanted version, or check if already done:

➜ ssh cluster3-node1

➜ root@cluster3-node1:~# apt update
Hit:1 http://ppa.launchpad.net/rmescandon/yq/ubuntu focal InRelease
Hit:3 http://us.archive.ubuntu.com/ubuntu bionic InRelease                 
Get:2 https://packages.cloud.google.com/apt kubernetes-xenial InRelease [8,993 B]
Fetched 8,993 B in 1s (17.8 kB/s)
Reading package lists... Done
Building dependency tree       
Reading state information... Done
3 packages can be upgraded. Run 'apt list --upgradable' to see them.

➜ root@cluster3-node1:~# apt-mark unhold kubeadm
kubeadm was already not hold.

➜ root@cluster3-node1:~# apt-mark hold kubectl kubelet
kubectl set on hold.
kubelet set on hold.

➜ root@cluster3-node1:~# apt install kubeadm=1.28.2-00
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
  kubeadm
1 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.
Need to get 10.3 MB of archives.
After this operation, 2,589 kB of additional disk space will be used.
Get:1 https://packages.cloud.google.com/apt kubernetes-xenial/main amd64 kubeadm amd64 1.28.2-00 [10.3 MB]
Fetched 10.3 MB in 1s (19.1 MB/s)
(Reading database ... 112527 files and directories currently installed.)
Preparing to unpack .../kubeadm_1.28.2-00_amd64.deb ...
Unpacking kubeadm (1.28.2-00) over (1.27.6-00) ...

Setting up kubeadm (1.28.2-00) ...

➜ root@cluster3-node1:~# apt-mark hold kubeadm
kubeadm set on hold.

➜ root@cluster3-node1:~# kubeadm upgrade node
[upgrade] Reading configuration from the cluster...
[upgrade] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[preflight] Running pre-flight checks
[preflight] Skipping prepull. Not a control plane node.
[upgrade] Skipping phase. Not a control plane node.
[upgrade] Backing up kubelet config file to /etc/kubernetes/tmp/kubeadm-kubelet-config1123040998/config.yaml
[kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[upgrade] The configuration for this node was successfully updated!
[upgrade] Now you should go ahead and upgrade the kubelet package using your package manager.

Now we follow that kubeadm told us in the last line and upgrade kubelet (and kubectl):

➜ root@cluster3-node1:~# apt-mark unhold kubectl kubelet
Canceled hold on kubectl.
Canceled hold on kubelet.

➜ root@cluster3-node1:~# apt install kubelet=1.28.2-00 kubectl=1.28.2-00
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
  kubectl kubelet
2 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 29.8 MB of archives.
After this operation, 5,194 kB of additional disk space will be used.
Get:1 https://packages.cloud.google.com/apt kubernetes-xenial/main amd64 kubectl amd64 1.28.2-00 [10.3 MB]
Get:2 https://packages.cloud.google.com/apt kubernetes-xenial/main amd64 kubelet amd64 1.28.2-00 [19.5 MB]
Fetched 29.8 MB in 2s (14.5 MB/s)   
(Reading database ... 112527 files and directories currently installed.)
Preparing to unpack .../kubectl_1.28.2-00_amd64.deb ...
Unpacking kubectl (1.28.2-00) over (1.27.6-00) ...
Preparing to unpack .../kubelet_1.28.2-00_amd64.deb ...
Unpacking kubelet (1.28.2-00) over (1.27.6-00) ...
Setting up kubectl (1.28.2-00) ...
Setting up kubelet (1.28.2-00) ...

➜ root@cluster3-node1:~# service kubelet restart

➜ root@cluster3-node1:~# service kubelet status
● kubelet.service - kubelet: The Kubernetes Node Agent
     Loaded: loaded (/lib/systemd/system/kubelet.service; enabled; vendor preset: enabled)
    Drop-In: /etc/systemd/system/kubelet.service.d
             └─10-kubeadm.conf
     Active: active (running) since Tue 2023-09-26 12:56:19 UTC; 4s ago
       Docs: https://kubernetes.io/docs/home/
   Main PID: 34075 (kubelet)
      Tasks: 9 (limit: 1066)
     Memory: 26.4M
     CGroup: /system.slice/kubelet.service
...

Looking good, what does the node status say?

➜ k get node
NAME                     STATUS                     ROLES           AGE    VERSION
cluster3-controlplane1   Ready                      control-plane   154m   v1.28.2
cluster3-node1           Ready,SchedulingDisabled   <none>          147m   v1.28.2

Beautiful, let's make it schedulable again:

➜ k uncordon cluster3-node1
node/cluster3-node1 uncordoned

➜ k get node
NAME                     STATUS   ROLES           AGE    VERSION
cluster3-controlplane1   Ready    control-plane   154m   v1.28.2
cluster3-node1           Ready    <none>          147m   v1.28.2

We're up to date.

第二十一题: Image Vulnerability Scanning

问题

Task weight: 2%

(can be solved in any kubectl context)

The Vulnerability Scanner trivy is installed on your main terminal. Use it to scan the following images for known CVEs:

  • nginx:1.16.1-alpine
  • k8s.gcr.io/kube-apiserver:v1.18.0
  • k8s.gcr.io/kube-controller-manager:v1.18.0
  • docker.io/weaveworks/weave-kube:2.7.0

Write all images that don't contain the vulnerabilities `CVE-2020-10878 orCVE-2020-1967into/opt/course/21/good-images`.

解答

The tool trivy is very simple to use, it compares images against public databases.

➜ trivy nginx:1.16.1-alpine
2020-10-09T20:59:39.198Z        INFO    Need to update DB
2020-10-09T20:59:39.198Z        INFO    Downloading DB...
18.81 MiB / 18.81 MiB [-------------------------------------
2020-10-09T20:59:45.499Z        INFO    Detecting Alpine vulnerabilities...

nginx:1.16.1-alpine (alpine 3.10.4)
===================================
Total: 7 (UNKNOWN: 0, LOW: 0, MEDIUM: 7, HIGH: 0, CRITICAL: 0)

+---------------+------------------+----------+-------------------
|    LIBRARY    | VULNERABILITY ID | SEVERITY | INSTALLED VERSION
+---------------+------------------+----------+-------------------
| libcrypto1.1  | CVE-2020-1967    | MEDIUM   | 1.1.1d-r2         
... 

To solve the task we can run:

➜ trivy nginx:1.16.1-alpine | grep -E 'CVE-2020-10878|CVE-2020-1967'
| libcrypto1.1  | CVE-2020-1967    | MEDIUM   
| libssl1.1     | CVE-2020-1967    |          

➜ trivy k8s.gcr.io/kube-apiserver:v1.18.0 | grep -E 'CVE-2020-10878|CVE-2020-1967'
| perl-base     | CVE-2020-10878      | HIGH

➜ trivy k8s.gcr.io/kube-controller-manager:v1.18.0 | grep -E 'CVE-2020-10878|CVE-2020-1967'
| perl-base     | CVE-2020-10878      | HIGH   

➜ trivy docker.io/weaveworks/weave-kube:2.7.0 | grep -E 'CVE-2020-10878|CVE-2020-1967'
➜

The only image without the any of the two CVEs is docker.io/weaveworks/weave-kube:2.7.0, hence our answer will be:

#/opt/course/21/good-images
docker.io/weaveworks/weave-kube:2.7.0

第二十二题: Manual Static Security Analysis

问题

Task weight: 3%

(can be solved in any kubectl context)

The Release Engineering Team has shared some YAML manifests and Dockerfiles with you to review. The files are located under /opt/course/22/files.

As a container security expert, you are asked to perform a manual static analysis and find out possible security issues with respect to unwanted credential exposure. Running processes as root is of no concern in this task.

Write the filenames which have issues into `/opt/course/22/security-issues.

NOTE: In the Dockerfile and YAML manifests, assume that the referred files, folders, secrets and volume mounts are present. Disregard syntax or logic errors.

解答

We check location /opt/course/22/files and list the files.

➜ ls -la /opt/course/22/files
total 48
drwxr-xr-x 2 k8s k8s 4096 Sep 16 19:08 .
drwxr-xr-x 3 k8s k8s 4096 Sep 16 19:08 ..
-rw-r--r-- 1 k8s k8s  692 Sep 16 19:08 Dockerfile-go
-rw-r--r-- 1 k8s k8s  897 Sep 16 19:08 Dockerfile-mysql
-rw-r--r-- 1 k8s k8s  743 Sep 16 19:08 Dockerfile-py
-rw-r--r-- 1 k8s k8s  341 Sep 16 19:08 deployment-nginx.yaml
-rw-r--r-- 1 k8s k8s  705 Sep 16 19:08 deployment-redis.yaml
-rw-r--r-- 1 k8s k8s  392 Sep 16 19:08 pod-nginx.yaml
-rw-r--r-- 1 k8s k8s  228 Sep 16 19:08 pv-manual.yaml
-rw-r--r-- 1 k8s k8s  188 Sep 16 19:08 pvc-manual.yaml
-rw-r--r-- 1 k8s k8s  211 Sep 16 19:08 sc-local.yaml
-rw-r--r-- 1 k8s k8s  902 Sep 16 19:08 statefulset-nginx.yaml

We have 3 Dockerfiles and 7 Kubernetes Resource YAML manifests. Next we should go over each to find security issues with the way credentials have been used.

NOTE: You should be comfortable with Docker Best Practices and the Kubernetes Configuration Best Practices.

While navigating through the files we might notice:

Number 1

File Dockerfile-mysql might look innocent on first look. It copies a file secret-token over, uses it and deletes it afterwards. But because of the way Docker works, every RUN, COPY and ADD command creates a new layer and every layer is persistet in the image.

This means even if the file secret-token get's deleted in layer Z, it's still included with the image in layer X and Y. In this case it would be better to use for example variables passed to Docker.

# /opt/course/22/files/Dockerfile-mysql
FROM ubuntu

# Add MySQL configuration
COPY my.cnf /etc/mysql/conf.d/my.cnf
COPY mysqld_charset.cnf /etc/mysql/conf.d/mysqld_charset.cnf

RUN apt-get update && \
    apt-get -yq install mysql-server-5.6 &&

# Add MySQL scripts
COPY import_sql.sh /import_sql.sh
COPY run.sh /run.sh

# Configure credentials
COPY secret-token .                                       # LAYER X
RUN /etc/register.sh ./secret-token                       # LAYER Y
RUN rm ./secret-token # delete secret token again         # LATER Z

EXPOSE 3306
CMD ["/run.sh"]

So we do:

echo Dockerfile-mysql >> /opt/course/22/security-issues

Number 2

The file deployment-redis.yaml is fetching credentials from a Secret named mysecret and writes these into environment variables. So far so good, but in the command of the container it's echoing these which can be directly read by any user having access to the logs.

# /opt/course/22/files/deployment-redis.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: mycontainer
        image: redis
        command: ["/bin/sh"]
        args:
        - "-c"
        - "echo $SECRET_USERNAME && echo $SECRET_PASSWORD && docker-entrypoint.sh" # NOT GOOD
        env:
        - name: SECRET_USERNAME
          valueFrom:
            secretKeyRef:
              name: mysecret
              key: username
        - name: SECRET_PASSWORD
          valueFrom:
            secretKeyRef:
              name: mysecret
              key: password

Credentials in logs is never a good idea, hence we do:

echo deployment-redis.yaml >> /opt/course/22/security-issues

Number 3

In file statefulset-nginx.yaml, the password is directly exposed in the environment variable definition of the container.

# /opt/course/22/files/statefulset-nginx.yaml
...
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: k8s.gcr.io/nginx-slim:0.8
        env:
        - name: Username
          value: Administrator
        - name: Password
          value: MyDiReCtP@sSw0rd               # NOT GOOD
        ports:
        - containerPort: 80
          name: web
..

This should better be injected via a Secret. So we do:

echo statefulset-nginx.yaml >> /opt/course/22/security-issues
➜ cat /opt/course/22/security-issues

Dockerfile-mysql
deployment-redis.yaml
statefulset-nginx.yaml

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