Wallos is an open-source, self-hostable personal subscription tracker. Prior to version 4.9.4, login.php generates an OIDC state nonce stored in $_SESSION['oidc_state'], but checksession.php dispatches the OIDC callback without comparing the incoming state against the session value. An attacker can trick a victim into visiting a crafted URL, causing Wallos to exchange the attacker's authorization code and log the victim into the attacker's account. This issue has been patched in version 4.9.4.