CVE-2026-54089: File Browser authentication bypass via forged proxy headers

Executive brief

File Browser is a web-based file management utility. When configured to use a reverse proxy for authentication, it fails to verify the source of identity headers, allowing any network-based attacker to impersonate any user, including administrators. This can lead to a total compromise of the file server, unauthorized access to all stored data, and the ability to execute arbitrary commands if shell features are enabled.

Technical details

The vulnerability exists in the `ProxyAuth.Auth()` function within `auth/proxy.go`. When `auth.method` is set to `proxy`, the application unconditionally trusts the username provided in a configured HTTP header (e.g., `X-Remote-User`) without verifying the request's origin or requiring a shared secret. An attacker can reach the File Browser service directly (bypassing the intended reverse proxy) and provide an arbitrary username to receive a valid JWT. If the provided username does not exist, the application automatically creates a new account with default permissions. This allows for full administrative takeover and unauthorized access to the filesystem.

Affected products

• File Browser File Browser >= 2.0.0-rc.1, <= 2.63.18

Timeline

• 2026-06-03: disclosed: Initial disclosure on GitHub Advisory Database
• 2026-07-10: advisory: Advisory updated with CVE-2026-54089

References

• https://api.github.com/users/Akokonunes
• https://github.com/Akokonunes
• https://api.github.com/users/Akokonunes/gists%7B/gist_id%7D
• https://api.github.com/users/Akokonunes/repos
• https://avatars.githubusercontent.com/u/46332131?v=4
• https://api.github.com/users/Akokonunes/events%7B/privacy%7D