CVE-2026-15013: Signature Bypass (CVSS 9.8)

Description

The SAML Single Sign On – SSO Login plugin for WordPress is vulnerable to Authentication Bypass via SAML Signature Algorithm Confusion in all versions up to, and including, 5.4.3. The vulnerability exists because `Mo_SAML_Utilities::mo_saml_cast_key()` reads the `SignatureMethod` Algorithm attribute directly from the attacker-controlled `SAMLResponse` parameter rather than enforcing the locally configured algorithm, causing the plugin to recast the IdP's RSA public key as an HMAC-SHA1 shared secret and validate the forged signature against it. This makes it possible for unauthenticated attackers to forge a SAML assertion targeting any WordPress account — including administrators — obtain valid WordPress authentication cookies, and achieve full administrator-level account takeover.

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CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0041

Probability of exploitation

0.34%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-347 CWE-347

References

Other References

https://plugins.trac.wordpress.org/browser/miniorange-saml-20-single-sign-on/tags/5.4.3/class-mo-saml-login-validate.php#L119 https://plugins.trac.wordpress.org/browser/miniorange-saml-20-single-sign-on/tags/5.4.3/class-mo-saml-utilities.php#L416 https://plugins.trac.wordpress.org/browser/miniorange-saml-20-single-sign-on/tags/5.4.3/class-mo-saml-utilities.php#L444 https://plugins.trac.wordpress.org/browser/miniorange-saml-20-single-sign-on/tags/5.4.3/class-mo-saml-utilities.php#L561 https://plugins.trac.wordpress.org/browser/miniorange-saml-20-single-sign-on/tags/5.4.3/includes/lib/SAML2Core/class-mo-saml-xml-security-key.php#L722 https://plugins.trac.wordpress.org/changeset?reponame=&old=3601345%40miniorange-saml-20-single-sign-on&new=3601345%40miniorange-saml-20-single-sign-on https://www.wordfence.com/threat-intel/vulnerabilities/id/ee95092d-6351-4612-872d-284165bc1201?source=cve

Frequently Asked Questions

What is CVE-2026-15013? +

The SAML Single Sign On – SSO Login plugin for WordPress is vulnerable to Authentication Bypass via SAML Signature Algorithm Confusion in all versions up to, and including, 5.4.3. The vulnerability exists because `Mo_SAML_Utilities::mo_saml_cast_key()` reads the `SignatureMethod` Algorithm attribute directly from the attacker-controlled `SAMLResponse` parameter rather than enforcing the locally configured algorithm, causing the plugin to recast the IdP's RSA public key as an HMAC-SHA1 shared secret and validate the forged signature against it. This makes it possible for unauthenticated attackers to forge a SAML assertion targeting any WordPress account — including administrators — obtain valid WordPress authentication cookies, and achieve full administrator-level account takeover. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-15013? +

CVE-2026-15013 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0041, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-15013? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-15013