A potential risk in kruise that could lead to takeover of the cluster[BUG] YOUR_TITLE

[HouqiyuA]

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 have reported the relevant problem to your team's private email （[email protected]） a few days ago, I am not sure whether your team has received it, so I raise this issue here. I hope you will forgive me if there is anything wrong.

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/ 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

[furykerry]

@HouqiyuA thanks for your feedback, kruise involves two componenets, the central management component: kruise-manager, and the node management component kruise-daemon. Kruise manager do have the cluster level secret list privilege, and it should be managed carefully, just like the kubenetes controller manager, preferably in a separate node pool. However the kruise-daemon only have namespace level secret list privilege, just as your suggested. In most cases, an attacker may escape the normal application, and gain the privileges of kruise-daemon, but that only leads to kruise-system namespace privilege, not the kruise-manager one. As for the kruise-manager, we will add more instruction in our site about the safe deployment setting, so as to mitigate the risk of cluster level privilege elevation