A potential risk in kcp that could lead to takeover of the clusterfeature:

[HouqiyuA]

Feature Description

Dear Team Members:

Greetings! Our team is very interested in your project and we recently identified a potential RBAC security risk while doing a security assessment of your project. Therefore, we would like to report it to you and provide you with the relevant details so that you can fix and improve it accordingly. I couldn't find a private email to report security risks, so I raised this issue. If there is anything inappropriate about it, I hope you can forgive me.
Details:

In this Kubernetes project, there exists a ClusterRole that has been granted list secrets high-risk permissions. These permissions allow the role to list confidential information across the cluster. An attacker could impersonate the ServiceAccount bound to this ClusterRole and use its high-risk permissions to list secrets information across the cluster. By combining the permissions of other roles, an attacker can elevate the privileges and further take over the entire cluster.

we constructed the following attack vectors.

First, you need to get a token for the ServiceAccount that has this high-risk privilege. If you are already in a Pod and have this override, you can directly run the following command to get the token: cat /var/run/secrets/[kubernetes.io/serviceaccount/](http://kubernetes.io/serviceaccount/) token. If you are on a node other than a Pod, you can run the following command to get the kubectl describe secret .

Use the obtained token information to authenticate with the API server. By including the token in the request, you can be recognized as a legitimate user with a ServiceAccount and gain all privileges associated with the ServiceAccount. As a result, this ServiceAccount identity can be used to list all secrets in the cluster.

We give two ways to further utilize ServiceAccount Token with other privileges to take over the cluster:

Method 1: Elevation of Privilege by Utilizing ServiceAccount Token Bound to ClusterAdmin

Directly use a Token with the ClusterAdmin role permissions that has the authority to control the entire cluster. By authenticating with this token, you can gain full control of the cluster.

Method 2: Create Privileged Containers with ServiceAccount Token with create pods permission You can use this ServiceAccount Token to create a privileged container that mounts the root directory and schedules it to the master node in a taint-tolerant way, so that you can access and leak the master node's kubeconfig configuration file. In this way you can take over the entire cluster.

For the above attack chain we have developed exploit code and uploaded it to github: https://github.com/HouqiyuA/k8s-rbac-poc
Mitigation methods are explored:

Carefully evaluate the permissions required for each user or service account to ensure that it is following the principle of least privilege and to avoid over-authorization.

If list secrets is a required permission, consider using more granular RBAC rules. Role Binding can be used to grant list secrets permissions instead of ClusterRole, which restricts permissions to specific namespaces or resources rather than the entire cluster.

Isolate different applications into different namespaces and use namespace-level RBAC rules to restrict access. This reduces the risk of privilege leakage across namespaces

Looking forward to hearing from you and discussing this risk in more detail with us, thank you very much for your time and attention.

Best wishes.

HouqiyuA

Proposed Solution

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Alternative Solutions

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Additional Context

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[embik]

Thank you for your report @HouqiyuA.

Given the scatter of issues across different Kubernetes-related projects, it's not clear to me how much awareness of kcp in specific you have. kcp does not support creating Pods, the workload part of Kubernetes is removed because it focuses on an API use-case.

Your concern of course is related to ServiceAccounts, not Pods. While the described scenario is accurate, we don't see this as grave in kcp because there is no way to launch privileged Pods (to take over underlying nodes) - that functionality doesn't exist. In addition, kcp separates users by workspaces which have their own RBAC - so cluster-admin in a workspace means you can only interact with resources in that workspace. We generally consider workspace owners to be responsible for giving out minimal permissions.

It's a good idea to raise awareness for this topic in the broader ecosystem, but I don't think we consider this a security issue. A note in our documentation might be worth it to explain the risk to workspace owners, if you are interested.

Since the PoC code clearly does not relate to kcp, I'll go ahead and close this ticket. Feel free to follow-up with a kcp-specific threat model that goes beyond misconfiguration (which, again, we should educate users against).