CVE-2026-86304: Signature Bypass (CVSS 9.8)

Description

MojoX::Authentication versions before 0.006 for Perl allow SAML authentication bypass because parse_assertion builds Net::SAML2::Binding::POST without a trust anchor. parse_assertion in MojoX::Authentication::Model::SAML2 calls Net::SAML2::Binding::POST->new with no cacert, cert_text or anchors argument, then passes the returned XML to Net::SAML2::Protocol::Assertion->new_from_xml with the IdP signing certificate as cacert. In Net::SAML2 before 0.86 that certificate guards only encrypted assertions, so the signature on an unencrypted assertion is checked against the certificate the response itself carries. An attacker starts a SAML login, then posts a response signed with a certificate of their own. The audience, InResponseTo and timestamp checks that follow are all satisfiable by the attacker, so the response authenticates any NameID it carries.

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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

0.0023

Probability of exploitation

0.13%

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://metacpan.org/release/POLETTIX/MojoX-Authentication-0.004/source/lib/MojoX/Authentication/Model/SAML2.pm#L188 https://metacpan.org/release/POLETTIX/MojoX-Authentication-0.006/source/Changes https://www.cve.org/CVERecord?id=CVE-2026-18089

Frequently Asked Questions

What is CVE-2026-86304? +

MojoX::Authentication versions before 0.006 for Perl allow SAML authentication bypass because parse_assertion builds Net::SAML2::Binding::POST without a trust anchor. parse_assertion in MojoX::Authentication::Model::SAML2 calls Net::SAML2::Binding::POST->new with no cacert, cert_text or anchors argument, then passes the returned XML to Net::SAML2::Protocol::Assertion->new_from_xml with the IdP signing certificate as cacert. In Net::SAML2 before 0.86 that certificate guards only encrypted assertions, so the signature on an unencrypted assertion is checked against the certificate the response itself carries. An attacker starts a SAML login, then posts a response signed with a certificate of their own. The audience, InResponseTo and timestamp checks that follow are all satisfiable by the attacker, so the response authenticates any NameID it carries. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-86304? +

CVE-2026-86304 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 0.0023, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-86304? +

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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