GHSA-3jp4-mhh4-gcgr Kimai has an Open Redirect via Unvalidated RelayState in SAML ACS Handler

• Packagist kimai/kimai: < 2.53.0 → fixed in 2.53.0

Summary The SAML authentication success handler in Kimai returns the `RelayState` POST parameter as a redirect destination without validating the host or scheme. After a user successfully authenticates via SAML, they are redirected to an attacker-controlled URL if the IdP includes a malicious `RelayState` value. This enables phishing attacks that steal credentials or session tokens post-SSO. *Requires SAML to be enabled (non-default configuration).* Details Vulnerable file: `src/Saml/Security/SamlAuthenticationSuccessHandler.php` ```php // Line 27-33 $relayState = $request->request->get('RelayState', $request->query->get('RelayState')); if (\is_scalar($relayState)) { $relayState = (string) $relayState; if ($relayState !== $this->httpUtils->generateUri($request, (string) $this->options['login_path'])) { return $relayState; // No host/scheme validation — any URL accepted } } ``` The only check is that `RelayState` does not equal the configured `login_path`. Any external URL (e.g., `https://attacker.com`) passes this check and is returned as the redirect destination. The existing unit test `SamlAuthenticationSuccessHandlerTest::testRelayState()` confirms this behavior — an absolute URL in `RelayState` results in a redirect to that URL with no restriction. Steps to Reproduce ``` 1. Enable SAML authentication in Kimai 2. Configure a SAML IdP (e.g., SimpleSAMLphp) 3. Initiate IdP-initiated SSO with RelayState=https://attacker.com — or intercept the ACS POST and modify RelayState to https://attacker.com 4. Complete SAML authentication at the IdP 5. Observe: after the SAMLResponse POST to /saml/acs, Kimai issues: HTTP/1.1 302 Found Location: https://attacker.com ``` Code-confirmed via unit test (`testRelayState`): `onAuthenticationSuccess` with `RelayState=http://localhost/relayed` redirects directly to that URL. External URLs follow the same code path. Impact While this bug exists it has low practical possibilities and the attacker needs to be able to create a SAML request, meaning either admin access to an IdP supporting such an action OR access to the private SAML keys / certificates. In other words: only exploitable in IdP-initiated SSO flows where the IdP includes a `RelayState` value supplied by the attacker (e.g., via a malicious link to the IdP). Fix The `RelayState` is validated before redirecting, see #5878 • It may not contain a host or port and cannot start with `//`. • If it contains a host, it must match the current host.