SAML Single Sign On <= 5.4.6 - Unauthenticated Authentication Bypass via X.509 Certificate Poisoning

Summary

The SAML Single Sign On – SSO Login plugin for WordPress is vulnerable to Authentication Bypass in versions up to, and including, 5.4.6. This is due to the mo_saml_login_validate() ACS handler persisting the X.509 certificate extracted from an incoming SAMLResponse into the mo_saml_required_certificate option before the signature-validation verdict is enforced, because mo_saml_find_certificate() returns false on a fingerprint mismatch rather than halting execution. This makes it possible for unauthenticated attackers to overwrite the plugin's stored IdP signing certificate with an attacker-controlled value, and subsequently forge SAML assertions for any WordPress account — including administrators — to obtain a fully privileged session. Note: The exploit requires the administrator to perform a repair after receiving the test_config_error_wpsamlerr004 error message during the test configuration.

Timeline

1. Aug 29, 2026, 5:25 PM UTCCVE published
2. Aug 31, 2026, 6:04 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Aug 31, 2026, 6:10 PM UTCRecord last updated

Affected versions

• cyberlord92 SAML Single Sign On – SSO Login

  through 5.4.6

References 5