[Security Advisory] CVE-2023-3893: Insufficient input sanitization on kubernetes-csi-proxy leads to privilege escalation

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Rita Zhang

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Aug 23, 2023, 10:27:43 AM8/23/23
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Hello Kubernetes Community,


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


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-2023-3893**


Am I vulnerable?


Any kubernetes environment with Windows nodes that are running kubernetes-csi-proxy is impacted.  This is a common default configuration on Windows nodes.  Run `kubectl get nodes -l kubernetes.io/os=windows` to see if any Windows nodes are in use.


Affected Versions


- kubernetes-csi-proxy <= v2.0.0-alpha.0

- kubernetes-csi-proxy <= v1.1.2


How do I mitigate this vulnerability?


The provided patch fully mitigates the vulnerability and has no known side effects.  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 provided patch, there are no known mitigations to this vulnerability.


Fixed Versions


- kubernetes-csi-proxy v2.0.0-alpha.1

- kubernetes-csi-proxy v1.1.3


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


To upgrade: cordon the node, stop the associated Windows service, replace the csi-proxy.exe binary, restart the associated Windows service, and un-cordon the node.  See the installation docs for more details: https://github.com/kubernetes-csi/csi-proxy#installation

If a Windows host process daemon set is used to run kubernetes-csi-proxy such as https://github.com/kubernetes-csi/csi-driver-smb/blob/master/charts/latest/csi-driver-smb/templates/csi-proxy-windows.yaml, simply upgrade the image to a fixed version such as ghcr.io/kubernetes-sigs/sig-windows/csi-proxy:v1.1.3


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 secu...@kubernetes.io


Additional Details


See the GitHub issue for more details: https://github.com/kubernetes/kubernetes/issues/119594


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:

Mauricio Poppe @mauriciopoppe


Thank You,

Rita Zhang on behalf of the Kubernetes Security Response Committee



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