criticalCVE-2026-15981

SAML Single Sign On <= 5.4.4 - Unauthenticated Authentication Bypass via SAMLResponse Parameter

Q: What is affected by CVE-2026-15981?

cyberlord92 SAML Single Sign On – SSO Login versions listed as affected should be reviewed: <= 5.4.4, up to and including 5.4.4.

Q: What should I fix first?

Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.

Q: How do I confirm the fix worked?

Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.

Q: How are Fixnx security risk categories chosen?

Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.

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.

Browse WordPress security risks

ProductSAML Single Sign On – SSO Login

CVSS9.8

EPSSNot scored yet

UpdatedJuly 24, 2026

Quick answer

cyberlord92 SAML Single Sign On – SSO Login should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.

Who is affected

Affected versions

<= 5.4.4
up to and including 5.4.4

Fixed versions

5.4.5

How to fix it

CVE-2026-15981 affects SAML Single Sign On – SSO Login and involves authentication bypass. Successful exploitation may let an attacker bypass an expected login or multi-factor authentication check. Treat this as a high-priority fix, especially when the affected component or endpoint is reachable by untrusted users. Upgrade SAML Single Sign On – SSO Login to 5.4.5 or a later vendor-supported fixed release.

Inventory every deployment, device, package, plugin, container, build, and environment that uses SAML Single Sign On – SSO Login.
Compare the installed version with the recorded affected range: <= 5.4.4, *-5.4.4.
Upgrade SAML Single Sign On – SSO Login to 5.4.5 or a later vendor-supported fixed release.
Until patched, disable the affected SAML Single Sign On – SSO Login feature or plugin and restrict its public and administrator endpoints.
Review configuration, roles, tokens, network paths, and exposed endpoints connected to SAML Single Sign On – SSO Login; remove access that is not required.
Review authentication, API, audit, and object-change logs for cross-user access, bypassed checks, or unexpected privileged actions.
If exploitation is suspected, isolate affected assets, preserve evidence, rotate exposed credentials or keys, restore trusted data, and rebuild compromised systems before returning them to service.

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Verify the fix

Confirm every affected asset now runs the fixed vendor-supported release or has the documented mitigation for CVE-2026-15981 in place.
Use a safe regression test to confirm the affected authentication bypass path no longer produces the vulnerable behavior.
Confirm temporary access controls, endpoint restrictions, network blocks, and least-privilege settings remain effective after the update.
Review post-remediation logs and rerun Fixnx plus the relevant package, dependency, firmware, browser, or product-specific security check.
Document affected assets, versions, changes, validation evidence, reviewed logs, and any credential rotation, cleanup, or replacement completed.

Related categories

WordPress PHP Authentication Bypass Cryptography SAML

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Trusted references

Source advisoryNVD, Wordfence Source advisoryNVD, Wordfence Source advisoryNVD, Wordfence Source advisoryNVD, Wordfence Source advisoryNVD, Wordfence Source advisoryNVD, Wordfence Source advisoryNVD, Wordfence Wordfence advisoryNVD, Wordfence Wordfence advisoryNVD, Wordfence

FAQ

What is affected by CVE-2026-15981?

cyberlord92 SAML Single Sign On – SSO Login versions listed as affected should be reviewed: <= 5.4.4, up to and including 5.4.4.

What should I fix first?

Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.

How do I confirm the fix worked?

Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.

How are Fixnx security risk categories chosen?

Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.