GitHub Security Advisory: GHSA-9xx5-cv6j-x533
Package: admidio/admidio (COMPOSER)
Severity: MODERATE (CVSS 6.8)
CWE: CWE-287: Improper Authentication
Vulnerable versions: <= 5.0.8
Patched in: 5.0.9

Summary: Admidio: OIDC Token Introspection Endpoint Returns Active for All Tokens Without Validation

Details:
## Summary

The OIDC token introspection endpoint (`/modules/sso/index.php/oidc/introspect`) always returns `{"active": true}` for every request, regardless of whether a valid token is provided, whether the token is expired, revoked, or completely fabricated. The endpoint performs no authentication of the calling resource server and no validation of the submitted token. Any resource server that relies on this introspection endpoint to validate access tokens will accept all requests as authorized, enabling complete authentication bypass.

Additionally, the OIDC token revocation endpoint (`/oidc/revoke`) returns `{"revoked": true}` without actually revoking any token, preventing resource servers from invalidating compromised credentials.

## Details

The vulnerability is in `src/SSO/Service/OIDCService.php`, lines 604-619:

```php
public function handleIntrospectionRequest() {
    // TODO_RK
    if (!$this->isServiceSetup) {
        $this->setupService();
    }
    return new JsonResponse(["active" => true]);
}

public function handleRevocationRequest() {
    // TODO_RK
    if (!$this->isServiceSetup) {
        $this->setupService();
    }

    return new JsonResponse(["revoked" => true]);
}
```

The introspection endpoint is routed at `modules/sso/index.php`, line 58-59:

```php
} elseif (strpos($requestUri, '/oidc/introspect') !== false) {
    $response = $oidcService->handleIntrospectionRequest();
```

The router comment at line 35 says "Login checks will be done in the individual endpoint handler functions!" but neither `handleIntrospectionRequest` nor `handleRevocationRequest` perform any authentication or authorization checks.

Per RFC 7662 (OAuth 2.0 Token Introspection), the introspection endpoint:
1. MUST authenticate the calling resource server (Section 2.1)
2. MUST validate the submitted token against its database
3. MUST return `{"active": false}` for invalid, expired, or revoked tokens

The current implementation violates all three requirements.

**Attack flow:**
1. Attacker obtains a resource server's endpoint URL that uses Admidio as its OIDC provider
2. Attacker crafts any arbitrary string as a Bearer token
3. Resource server sends the fabricated token to `/oidc/introspect` for validation
4. Admidio returns `{"active": true}` without any checks
5. Resource server accepts the fabricated token as valid and grants access

**The revocation bypass compounds this:** If a legitimate token is stolen, the resource server or client application cannot revoke it. Calling `/oidc/revoke` returns success without actually revoking the token in the database, so the stolen token remains usable indefinitely (until its expiry time).

## PoC

```bash
# Step 1: Confirm the introspection endpoint exists and always returns active
# No valid token needed - any string works
curl -X POST https://TARGET/modules/sso/index.php/oidc/introspect \
  -d "token=COMPLETELY_FABRICATED_TOKEN_12345"

# Expected response: {"active":true}

# Step 2: Try with an empty token