CVE-2026-107810: Nginx UI: Backup restore follows crafted symlinks into the live Nginx configuration path before restore flags are applied

### Summary An authenticated user who can create and restore a backup can craft a valid backup archive that causes the restore staging process to write attacker-controlled files into the live Nginx configuration path even when both `restore_nginx` and `restore_nginx_ui` are set to `false`. ### Details The restore flow always extracts the outer archive, verifies the manifest, decrypts `nginx-ui.zip` and `nginx.zip`, and extracts both inner archives before it decides whether `RestoreNginx` or `RestoreNginxUI` should be applied. The zip extractor explicitly allows absolute symlinks when the link target is under `nginx.GetConfPath()` or `nginx.GetModulesPath()`. Later regular-file entries are then created with `os.OpenFile()` on the symlinked path, which follows the symlink and writes into the live path. Relevant code paths: - [internal/backup/restore.go](/home/kali/Desktop/bounty/nginx-ui/internal/backup/restore.go:39) - [internal/backup/restore.go](/home/kali/Desktop/bounty/nginx-ui/internal/backup/restore.go:79) - [internal/backup/restore.go](/home/kali/Desktop/bounty/nginx-ui/internal/backup/restore.go:204) - [internal/backup/restore.go](/home/kali/Desktop/bounty/nginx-ui/internal/backup/restore.go:286) - [api/backup/restore.go](/home/kali/Desktop/bounty/nginx-ui/api/backup/restore.go:31) - [api/backup/backup.go](/home/kali/Desktop/bounty/nginx-ui/api/backup/backup.go:15) This means the restore trust boundary is broken during extraction. A restore request that explicitly opted out of restoring either Nginx or Nginx UI can still modify the live Nginx configuration tree during staging. ### PoC I verified this locally in an isolated environment with a temporary package-level harness that exercised the real `Backup()` and `Restore()` implementations. What the executed test did: 1. Created a temporary `app.ini`, database file, and a temporary live Nginx config directory. 2. Called the real `Backup()` implementation to obtain a valid backup archive plus AES key/IV. 3. Extracted the outer backup, decrypted `nginx.zip`, replaced it with a crafted zip containing: - a symlink entry `link -> <live nginx conf dir>` - a later regular file entry `link/poc.conf` 4. Recomputed `manifest.json` size/hash values for the modified encrypted `nginx.zip` and re-signed `manifest.sig` with the expected signing key derived from the AES key. 5. Repacked the outer archive and called the real `Restore()` implementation with: - `RestoreNginx: false` - `RestoreNginxUI: false` 6. Verified that `<live nginx conf dir>/poc.conf` was created anyway. Observed result from the actual local verification: - The crafted restore completed successfully with both restore flags set to `false`. - The asserted sink was the existence and content of the live-path file written during restore staging. ### Impact Any deployment that allows an authenticated user to create and restore backups is affected. A crafted restore archive can modify the live Nginx configuration path before either restore toggle is honored. This can lead to persistent configuration injection, denial of service on a later reload, or other follow-on impact depending on what files the deployment later consumes from the modified path.