CVE-2026-62685: File Browser: Colliding username normalization gives two users the same home directory

FileBrowser confines each user to a scope: a home directory that acts as the boundary for everything they can read or write. When self-registration and automatic home-directory creation are both enabled (Signup=true and CreateUserDir=true), a new user’s scope is built from their username after it passes through cleanUsername(). That function rewrites the name: it strips .. and replaces every character outside 0-9A-Za-z@_\-. with -.

The problem is that this rewrite is many-to-one: different usernames can produce the same result, and FileBrowser never checks whether the resulting scope is already taken. So team/one, team one, and team-one all collapse to the same directory name, and whoever registers second is handed the same home directory as the first user instead of an isolated one.

This breaks per-user isolation. An attacker can pick a username that normalizes onto a victim’s directory (for example registering alice/ or al..ice to land in alice’s home) and gain full read and write access to that victim’s files. Because username uniqueness is enforced on the raw name, both accounts coexist normally and neither user is warned that they share storage.