CVE-2026-54910: FileBrowser Quantum's path traversal issue in subtitle handler allows any authenticated user to read arbitrary files

The subtitlesHandler endpoint (GET /api/media/subtitles) accepts two user-controlled query parameters: path and name, both of which are used in filesystem operations without sanitization, creating two independent path traversal vectors.

The primary vector is the path parameter: it is passed directly to idx.GetRealPath() without calling SanitizeUserPath(), allowing an attacker to escape the storage root and set parentDir to any directory on the host. No existing anchor file is required.

The secondary vector is the name parameter: it is joined with parentDir via filepath.Join(parentDir, name) without stripping directory components, allowing traversal relative to any resolved parentDir.

Any authenticated user (regardless of role or permissions) can exploit either vector to read any text file readable by the server process, including /etc/passwd, SSH keys, database credentials, and JWT signing keys.