CVE-2026-25705: Rancher Extensions have arbitrary file access via path traversal

A vulnerability has been identified in Rancher’s Extensions where malicious code can be injected in Rancher through a path traversal in the compressedEndpoint field inside a UIPlugin deployment. A malicious UI extension could abuse that to:

• Overwrite Rancher binaries or configuration to inject code.
• Write to /var/lib/rancher/ to tamper with cluster state.
• If hostPath volumes are mounted, write to the host node filesystem.
• Use this issue to chain with other attack vectors.

By default only the administrator can deploy UI extensions, unless permissions are granted to other users. It’s always recommended to only install extensions that come from sources trusted by the user.

Please consult the associated MITRE CAPEC-126 - Technique - Path Traversal for further information about this category of attack.