CVE-2026-49283

Vulnerability Description

The SimpleSAMLphp SAML2 library is a PHP library for SAML2 related functionality. Prior to versions 4.19.3, 4.20.2, 5.0.6, and 6.2.1, the HTTPArtifact::receive() flow can treat an unsigned embedded SAML Response as cryptographically valid for the wrong identity provider. SOAPClient::addSSLValidator() attaches a TLS-based validator to the outer SOAP ArtifactResponse, while the embedded Response receives a validator that delegates to the outer message and is later checked against metadata selected from the embedded response issuer rather than necessarily the artifact issuer. SOAPClient::validateSSL() returns normally when the TLS public key does not match the key being validated, and SAML2\Message::validate() treats a validator call that does not throw as successful. In a multi-IdP federation, a malicious or lower-trust IdP can therefore provide an ArtifactResponse containing an unsigned Response that claims a higher-trust victim IdP as issuer and authenticate as arbitrary users with attacker-chosen assertion attributes, NameID, and session data. This issue is fixed in versions 4.19.3, 4.20.2, 5.0.6, and 6.2.1.

CVSS Score

Related Weaknesses (CWE)

References

• https://github.com/simplesamlphp/saml2/commit/4a71b20d8d845579fd0a54d6449c265b40
• https://github.com/simplesamlphp/saml2/commit/a2c1ac588c70d7b7998546cf32675fb113
• https://github.com/simplesamlphp/saml2/commit/d5c213132ef671c0018a11252322034dbd
• https://github.com/simplesamlphp/saml2/commit/e2df7992609964951b2a3e7d6566b7427b
• https://github.com/simplesamlphp/saml2/security/advisories/GHSA-6929-8p9f-26jx