CVE-2026-15981
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk43th percentile - higher than 43% of all known CVEs
Summary
The SAML Single Sign On – SSO Login plugin for WordPress up to version 5.4.4 is vulnerable to authentication bypass. The mo_saml_validate_signature() function performs a loose boolean check on openssl_verify() output, treating error -1 as truthy. An unauthenticated attacker can log in as any WordPress user, including administrators, by sending a crafted SAMLResponse with a deliberately malformed signature.
Risk Assessment
An attacker can gain full administrative access to WordPress, take over user accounts, and perform arbitrary actions.
Recommendation
Immediately update the SAML Single Sign On – SSO Login plugin to version 5.4.5 or later.
Original NVD description (English source)
The SAML Single Sign On – SSO Login plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 5.4.4. This is due to the mo_saml_validate_signature() function performing a loose boolean check on the raw tri-state integer returned by PHP's openssl_verify(), causing an error return value of -1 to be evaluated as truthy and therefore treated as a successful signature verification. This makes it possible for unauthenticated attackers to log in as any existing WordPress user, including administrators, by submitting a crafted SAMLResponse containing an attacker-controlled NameID and a deliberately malformed signature value that triggers an OpenSSL processing error — bypassing verification entirely and resulting in wp_set_auth_cookie() being called for the targeted account.