Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-08-29T18:16:36.313Z",
  "pubdate": "2026-08-29T18:16:36.313Z",
  "executiveSummary": "The SAML Single Sign On – SSO Login plugin for WordPress (versions up to and including 5.4.6) contains a critical authentication bypass vulnerability.\nThis vulnerability allows unauthenticated attackers to overwrite the Identity Provider (IdP) signing certificate stored within the plugin settings.\nBy manipulating the mo_saml_required_certificate option, an attacker can force the system to accept forged SAML assertions.\nThe exploit permits unauthorized access to any WordPress account, including administrator accounts, resulting in a full system compromise.\nThe attack is contingent upon specific configuration conditions, specifically requiring an administrator to trigger a repair process following a test_config_error_wpsamlerr004 error.\nThis flaw presents a severe security risk, as it bypasses standard SAML signature validation protocols, granting attackers total control over user authentication flows.",
  "technicalDetails": "The vulnerability resides within the mo_saml_login_validate() Assertion Consumer Service (ACS) handler. The flaw stems from an insecure order of operations where the plugin persists the X.509 certificate extracted from an incoming SAMLResponse into the global mo_saml_required_certificate option before the cryptographic verification of the SAML signature is completed.\nWhen the plugin processes an assertion, it calls mo_saml_find_certificate() to validate the incoming certificate against the stored configuration. However, if a fingerprint mismatch occurs, the function returns false rather than terminating the process or invalidating the session. Consequently, the untrusted certificate provided in the SAMLResponse payload is written to the plugin's configuration.\nThe exploitation flow begins with the attacker crafting a malicious SAMLResponse containing an arbitrary, attacker-controlled X.509 certificate. By submitting this payload to the ACS endpoint, the plugin updates its internal reference for the trusted IdP certificate to the attacker's public key.\nOnce the configuration is overwritten, the plugin trusts all subsequent SAML assertions signed by the attacker's corresponding private key. The process requires that an administrator encounters and attempts to resolve a test_config_error_wpsamlerr004 error, which serves as a catalyst for the plugin to process the injected configuration.\nPost-exploitation, the attacker can generate valid SAML assertions for any WordPress user account. Since the plugin's trust anchor has been modified to favor the attacker's certificate, the authentication process fails to identify the forgery. The plugin grants the attacker an authenticated session corresponding to the NameID field in the forged assertion. By specifying an administrator's identifier, the attacker gains full administrative privileges, allowing for arbitrary code execution, sensitive data exfiltration, or complete site takeover.\nThis vulnerability is particularly dangerous because it subverts the fundamental trust model of SAML, transforming the plugin from a security mechanism into a vehicle for privilege escalation and unauthorized account access."
}