GitLab has released patches to address a critical flaw impacting Community Edition (CE) and Enterprise Edition (EE) that could result in an authentication bypass. The vulnerability is rooted in the ruby-saml library (CVE-2024-45409, CVSS score: 10.0), which could allow an attacker to log in as an arbitrary user within the vulnerable system. It was addressed by the maintainers last week. The problem as a result of the library not properly verifying the signature of the SAML Response. SAML, short for Security Assertion Markup Language, is a protocol that enables single sign-on (SSO) and exchange of authentication and authorization data across multiple apps and websites. An unauthenticated attacker with access to any signed SAML document (by the IdP) can thus forge a SAML Response/Assertion with arbitrary contents, according to a security advisory. "This would allow the attacker to log in as arbitrary user within the vulnerable system.