oss-security - [kubernetes] CVE-2024-3177: Bypassing mountable secrets policy imposed by the ServiceAccount admission plugin

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Date: Tue, 16 Apr 2024 14:48:15 -0700
From: Rita Zhang <rita.z.zhang@...il.com>
To: oss-security@...ts.openwall.com
Subject: [kubernetes] CVE-2024-3177: Bypassing mountable secrets policy
 imposed by the ServiceAccount admission plugin

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 containers, init containers, and
ephemeral containers with the envFrom field populated. 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
containers, init containers, and ephemeral containers with the envFrom
field populated.

This issue has been rated Low CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N
<https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N>,
and assigned CVE-2024-3177

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 using containers, init containers, and ephemeral containers with
   the envFrom field populated.

Affected Versions

   -

   kube-apiserver v1.29.0 - v1.29.3
   -

   kube-apiserver v1.28.0 - v1.28.8
   -

   kube-apiserver <= v1.27.12

How do I mitigate this vulnerability?

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

Fixed Versions

   -

   kube-apiserver v1.29.4
   -

   kube-apiserver v1.28.9
   -

   kube-apiserver v1.27.13

These releases have been published today, April 16th, 2024.

Detection

Pod update requests using a container, init container, or ephemeral
container with the envFrom field populated that exploits this vulnerability
with unintended secret will be captured in API audit logs. You can also use
the following kubectl command to find active pods using the
kubernetes.io/enforce-mountable-secrets annotation.

`kubectl get serviceaccounts --all-namespaces -o jsonpath="{range
.items[?(@.metadata.annotations['kubernetes\.io/enforce-mountable-secrets']=='true')]}{.metadata.namespace}{'\t'}{.
metadata.name}{'\n'}{end}"`

Additional Details

See the GitHub issue for more details:
<https://github.com/kubernetes/kubernetes/issues/118640>
https://github.com/kubernetes/kubernetes/issues/124336

Acknowledgements

This vulnerability was reported by tha3e1vl.

The issue was fixed and coordinated by the fix team:

Rita Zhang @ritazh

Joel Smith @joelsmith

Mo Khan @enj

and release managers:

Sascha Grunert @saschagrunert

Jeremy Rickard @jeremyrickard

Thank You,

Rita Zhang on behalf of the Kubernetes Security Response Committee

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