Authentication bypass in SAML Single Sign On plugin for WordPress (CVE-2026-15981)

The SAML Single Sign On - SSO Login plugin for WordPress contains an authentication bypass vulnerability caused by the mo_saml_validate_signature() function performing a loose boolean check on the tri-state integer returned by PHP's openssl_verify(). An error return value of -1 is incorrectly evaluated as truthy, allowing the signature verification step to be bypassed entirely. Unauthenticated attackers can exploit this by submitting a crafted SAMLResponse with an attacker-controlled NameID and a malformed signature that triggers an OpenSSL error, resulting in arbitrary account takeover including administrator accounts. Affected versions: - <= 5.4.4 We recommend updating to: 5.4.5. CVSS 9.8 · our assessment: act_now Reference: https://www.wordfence.com/threat-intel/vulnerabilities/id/b412f60f-61ea-47b1-a3ef-17275f7951df?source=cve Details: https://vuln.today/cve/CVE-2026-15981