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CVE-2025-25291 is an authentication bypass vulnerability in ruby-saml, the Ruby library used to implement SAML SSO. The issue affects ruby-saml versions prior to 1.12.4 and 1.18.0. According to the provided content, the flaw is caused by an XML parser differential between REXML and Nokogiri, and specifically by ruby-saml validating signatures against a reserialized XML representation rather than the original attacker-supplied structure. The content states that during signature validation, ruby-saml flows through Response.is_valid() / validate() into signature validation logic that creates a new REXML::Document from self.to_s. Because parsing and round-tripping can change document structure, an attacker can craft a SAMLResponse whose signed content is interpreted one way during validation and another way during later application processing. This enables a SAML Signature Wrapping attack that can cause the service provider to accept a forged assertion while the signature check succeeds on different XML content.
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An authentication bypass vulnerability in ruby-saml affecting GitLab SAML SSO.
Critical vulnerability impacting GitLab SAML-based SSO that can enable authentication bypass and user impersonation (as described in the content).
A critical vulnerability in GitLab's SAML-based SSO authentication mechanism that allows attackers to bypass authentication and impersonate users.
A previously patched SAML-related authentication vulnerability referenced as part of GitLab's security history.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.