CVE-2026-15981: cyberlord92 saml single sign on – sso login Improper Authentication

Vulnerability summary

CVE-2026-15981 is a critical (CVSS 9.8) Improper Authentication vulnerability in cyberlord92 saml single sign on – sso login. EPSS estimates a 2.36% chance of exploitation in the next 30 days, higher than 83.6% of scored vulnerabilities. Fixed in 5.4.5.

Timeline

1. 23-07-2026
   PublishedVulnerability first disclosed.
2. 24-07-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-287Improper AuthenticationWhen an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.