CVE-2026-15981: 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_sig

criticalpublic exploitCVSS 9.8CVE-2026-15981

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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: critical — CVSS 9.8
Published: 2026-07-23
Last updated: 2026-07-24
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-15981

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-159810.55% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 43% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-15981	coverage & exploitation status	NVD · CVE.org

Recent advisories for SAML Single Sign

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

criticalCVE-2026-15013: The SAML Single Sign On – SSO Login plugin for WordPress is vulnerable to Authentication Bypas…nvd · 2026-07-16
highCVE-2026-31982: An Open Redirect vulnerability was discovered in the SAML Single Sign-On functionality due to …nvd · 2026-07-09

CVE-2026-15981: 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_sig

Details

Exploitation outlook

Referenced CVEs

Recent advisories for SAML Single Sign

More from NVD Recent CVEs