File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. In versions 2.61.2 and below, 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. The signupHandler is supposed to create unprivileged accounts for new visitors. It contains no explicit user.Perm.Admin = false reset after applying defaults. 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. This issue has been resolved in version 2.62.0.

Affected: Go: github.com/filebrowser/filebrowser/v2

## 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://loca…