oss-security - [kubernetes] CVE-2023-2728: Bypassing enforce mountable secrets policy imposed by the ServiceAccount admission plugin Rita Zhang <rita.z.zhang@...il.com>

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Date: Thu, 6 Jul 2023 14:27:49 -0700
From: Rita Zhang <rita.z.zhang@...il.com>
To: oss-security@...ts.openwall.com
Subject: [kubernetes] CVE-2023-2728: Bypassing enforce mountable secrets
 policy imposed by the ServiceAccount admission plugin Rita Zhang <rita.z.zhang@...il.com>

Hello Kubernetes Community,

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
<http://kubernetes.io/enforce-mountable-secrets>* annotation are used
together with ephemeral containers.

This issue has been rated *Medium* (
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
<https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N>),
and
assigned CVE-2023-2728

*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
   <http://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

These releases have been published today, June 14th, 2023.

*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.

*Additional Details*
See the GitHub issue for more details:
https://github.com/kubernetes/kubernetes/issues/118640

Thank You,
Rita Zhang on behalf of the Kubernetes Security Response Committee

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