[Security Advisory] CVE-2023-3955: Insufficient input sanitization on Windows nodes leads to privilege escalation

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Hello Kubernetes Community,

A security issue was discovered in Kubernetes where a user that can create pods on Windows nodes may be able to escalate to admin privileges on those nodes. Kubernetes clusters are only affected if they include Windows nodes.

This issue has been rated HIGH (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H - 8.8), and assigned CVE-2023-3955

Am I vulnerable?

Any kubernetes environment with Windows nodes is impacted. Run kubectl get nodes -l kubernetes.io/os=windows to see if any Windows nodes are in use.

Affected Versions

  • kubelet <= v1.28.0

  • kubelet <= v1.27.4

  • kubelet <= v1.26.7

  • kubelet <= v1.25.12

  • kubelet <= v1.24.16

How do I mitigate this vulnerability?

The provided patch fully mitigates the vulnerability (see fix impact below). Full mitigation for this class of issues requires patches applied for CVE-2023-3676, CVE-2023-3955, and CVE-2023-3893.

Outside of applying the patch, there are no known mitigations to this vulnerability.

Fixed Versions

  • kubelet v1.28.1

  • kubelet v1.27.5

  • kubelet v1.26.8

  • kubelet v1.25.13

  • kubelet v1.24.17

These releases will be published over the course of today, August 23rd, 2023.

Fix impact: Passing Windows Powershell disk format options to in-tree volume plugins will result in an error during volume provisioning on the node. There are no known use cases for this functionality, nor is this functionality supported by any known out-of-tree CSI driver.

To upgrade, refer to the documentation:

https://kubernetes.io/docs/tasks/administer-cluster/cluster-management/#upgrading-a-cluster

Detection

Kubernetes audit logs can be used to detect if this vulnerability is being exploited. Pod create events with embedded powershell commands are a strong indication of exploitation.

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

Additional Details

See the GitHub issue for more details: CVE-2023-3955: Insufficient input sanitization on Windows nodes leads to privilege escalation · Issue #119595 · kubernetes/kubernetes · GitHub

Acknowledgements

This vulnerability was discovered by James Sturtevant @jsturtevant and Mark Rossetti @marosset during the process of fixing CVE-2023-3676 (that original CVE was reported by Tomer Peled @tomerpeled92)

The issue was fixed and coordinated by the fix team:

James Sturtevant @jsturtevant

Mark Rossetti @marosset

Andy Zhang @andyzhangx

Justin Terry @jterry75

Kulwant Singh @KlwntSingh

Micah Hausler @micahhausler

Rita Zhang @ritazh

and release managers:

Jeremy Rickard @jeremyrickard

Thank You,

Rita Zhang on behalf of the Kubernetes Security Response Committee

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