CVE-2023-2727, CVE-2023-2728: Bypassing policies imposed by the ImagePolicyWebhook and bypassing mountable secrets policy imposed by the ServiceAccount admission plugin

[ritazh]

CVE-2023-2727: Bypassing policies imposed by the ImagePolicyWebhook admission plugin

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

A security issue was discovered in Kubernetes where users may be able to launch containers using images that are restricted by ImagePolicyWebhook when using ephemeral containers. Kubernetes clusters are only affected if the ImagePolicyWebhook admission plugin is used together with ephemeral containers.

Am I vulnerable?

Clusters are impacted by this vulnerability if all of the following are true:

1. The ImagePolicyWebhook admission plugin is used to restrict use of certain images
2. Pods are using ephemeral containers.

Affected Versions

• kube-apiserver v1.27.0 - v1.27.2
• kube-apiserver v1.26.0 - v1.26.5
• kube-apiserver v1.25.0 - v1.25.10
• kube-apiserver <= v1.24.14

How do I mitigate this vulnerability?

This issue can be mitigated by applying the patch provided for the kube-apiserver component. This patch prevents ephemeral containers from using an image that is restricted by ImagePolicyWebhook.

Note: Validation webhooks (such as Gatekeeper and Kyverno) can also be used to enforce the same restrictions.

Fixed Versions

• kube-apiserver v1.27.3
• kube-apiserver v1.26.6
• kube-apiserver v1.25.11
• kube-apiserver v1.24.15

Detection

Pod update requests using an ephemeral container with an image that should have been restricted by an ImagePolicyWebhook will be captured in API audit logs. You can also use kubectl get pods to find active pods with ephemeral containers running an image that should have been restricted in your cluster with this issue.

Acknowledgements

This vulnerability was reported by Stanislav Láznička, and fixed by Rita Zhang.

CVE-2023-2728: Bypassing enforce mountable secrets policy imposed by the ServiceAccount admission plugin

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

A security issue was discovered in Kubernetes where users may be able to launch containers that bypass the mountable secrets policy enforced by the ServiceAccount admission plugin when using ephemeral containers. The policy ensures pods running with a service account may only reference secrets specified in the service account’s secrets field. Kubernetes clusters are only affected if the ServiceAccount admission plugin and the kubernetes.io/enforce-mountable-secrets annotation are used together with ephemeral containers.

Am I vulnerable?

Clusters are impacted by this vulnerability if all of the following are true:

1. The ServiceAccount admission plugin is used. Most cluster should have this on by default as recommended in https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/#serviceaccount
2. The kubernetes.io/enforce-mountable-secrets annotation is used by a service account. This annotation is not added by default.
3. Pods are using ephemeral containers.

Affected Versions

• kube-apiserver v1.27.0 - v1.27.2
• kube-apiserver v1.26.0 - v1.26.5
• kube-apiserver v1.25.0 - v1.25.10
• kube-apiserver <= v1.24.14

How do I mitigate this vulnerability?

This issue can be mitigated by applying the patch provided for the kube-apiserver component. The patch prevents ephemeral containers from bypassing the mountable secrets policy enforced by the ServiceAccount admission plugin.

Fixed Versions

• kube-apiserver v1.27.3
• kube-apiserver v1.26.6
• kube-apiserver v1.25.11
• kube-apiserver v1.24.15

Detection

Pod update requests using an ephemeral container that exploits this vulnerability with unintended secret will be captured in API audit logs. You can also use kubectl get pods to find active pods with ephemeral containers running with a secret that is not referenced by the service account in your cluster.

Acknowledgements

This vulnerability was reported by Rita Zhang, and fixed by Rita Zhang.

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

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

[tamilselvan1102]

please describe the issue

[tamilselvan1102]

/triage needs-information

[ritazh]

Fix PRs:

• master: Add ephemeralcontainer to imagepolicy securityaccount admission plugin #118356
• v1.27: Automated cherry pick of #118356: Add ephemeralcontainer to imagepolicy securityaccount #118471
• v1.26: Automated cherry pick of #118356: Add ephemeralcontainer to imagepolicy securityaccount #118473
• v1.25: Automated cherry pick of #118356: Add ephemeralcontainer to imagepolicy securityaccount #118474
• v1.24: Automated cherry pick of #118356: Add ephemeralcontainer to imagepolicy securityaccount #118512

[BenTheElder]

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

[You have to place prow commands in a new comment, it ignores comment edit events when looking for slash commands to avoid unintentionally triggering them on comment edits]

[BenTheElder]

@tamilselvan1102 it is standard practice in Kubernetes that private security issues start as a placeholder issue with no details until the patch is released and the details are later edited in. They usually just say "placeholder issue" filed by an organization member.

[tamilselvan1102]

@BenTheElder
Understood, Thank you.

[jsafrane]

nit: it would be nice to acknowledge the issue reporter.

[ritazh]

Updated Acknowledgements section. Thanks!

[PushkarJ]

/retitle CVE-2023-2727,CVE-2023-2728: Bypassing policies imposed by the ImagePolicyWebhook and bypassing mountable secrets policy imposed by the ServiceAccount admission plugin

(To fix this issue kubernetes/website#47003 in RSS CVE feed by removing space after comma)

[PushkarJ]

/retitle CVE-2023-2727, CVE-2023-2728: Bypassing policies imposed by the ImagePolicyWebhook and bypassing mountable secrets policy imposed by the ServiceAccount admission plugin

(Resetting back to original as kubernetes/website#47003 is now fixed and accepts any number of spaces before and after comma)