CVSS Rating: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

A security issue was discovered in Kubernetes where users may have access to secure endpoints in the control plane network. Kubernetes clusters are only affected if an untrusted user can modify Node objects and send proxy requests to them.

Kubernetes supports node proxying, which allows clients of kube-apiserver to access endpoints of a Kubelet to establish connections to Pods, retrieve container logs, and more. While Kubernetes already validates the proxying address for Nodes, a bug in kube-apiserver made it possible to bypass this validation. Bypassing this validation could allow authenticated requests destined for Nodes to to the API server's private network.

Am I vulnerable?

Clusters are affected by this vulnerability if there are endpoints that the kube-apiserver has connectivity to that users should not be able to access. This includes:

• kube-apiserver is in a separate network from worker nodes
• localhost services

mTLS services that accept the same client certificate as nodes may be affected. The severity of this issue depends on the privileges & sensitivity of the exploitable endpoints.

Clusters that configure the egress selector to use a proxy for cluster traffic may not be affected.

Affected Versions

• Kubernetes kube-apiserver <= v1.25.3
• Kubernetes kube-apiserver <= v1.24.7
• Kubernetes kube-apiserver <= v1.23.13
• Kubernetes kube-apiserver <= v1.22.15

How do I mitigate this vulnerability?

Upgrading the kube-apiserver to a fixed version mitigates this vulnerability.

Aside from upgrading, configuring an egress proxy for egress to the cluster network can mitigate this vulnerability.

Fixed Versions

• Kubernetes kube-apiserver v1.25.4
• Kubernetes kube-apiserver v1.24.8
• Kubernetes kube-apiserver v1.23.14
• Kubernetes kube-apiserver v1.22.16

Fix impact: In some cases, the fix can break clients that depend on the nodes/proxy subresource, specifically if a kubelet advertises a localhost or link-local address to the Kubernetes control plane.

Detection

Node create & update requests may be included in the Kubernetes audit log, and can be used to identify requests for IP addresses that should not be permitted. Node proxy requests may also be included in audit logs.

If you find evidence that this vulnerability has been exploited, please contact security@kubernetes.io

Acknowledgements

This vulnerability was reported by Yuval Avrahami of Palo Alto Networks.

/area security
/kind bug
/committee security-response
/label official-cve-feed
/sig api-machinery
/area apiserver