Authentication Bypass in SAML Single Sign On WordPress Plugin

Publication date: 2026-07-23

Last updated on: 2026-07-23

Assigner: Wordfence

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.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-07-23

Last Modified

2026-07-23

Generated

2026-07-24

AI Q&A

2026-07-24

EPSS Evaluated

N/A

NVD

CVE-2026-15981

Affected Vendors & Products

Vendor	Product	Version / Range
miniorange	saml_single_sign_on	to 5.4.4 (inc)

Helpful Resources

Exploitability

CWE

KEV

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

Attack-Flow Graph

Executive Summary

This vulnerability is an authentication bypass in the SAML Single Sign On – SSO Login WordPress plugin up to version 5.4.4. The flaw occurs in the mo_saml_validate_signature() function, which incorrectly treats an OpenSSL error (-1) as a successful signature verification due to a loose boolean check. Attackers can exploit this by sending a crafted SAMLResponse with a malformed signature to log in as any WordPress user, including administrators, without valid credentials.

Impact Analysis

This vulnerability allows unauthenticated attackers to gain unauthorized access to WordPress accounts, including admin accounts. Attackers could take over websites, steal data, install malware, or perform other malicious actions. The high CVSS score (9.8) indicates severe impact with no privileges or user interaction required.

Mitigation Strategies

Update the SAML Single Sign On – SSO Login plugin to the latest version beyond 5.4.4 immediately. If an update is not available, consider disabling the plugin temporarily until a patch is released. Review WordPress user accounts for unauthorized access and remove any suspicious admin accounts.

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