The vulnerability CVE-2025-25292 affects the ruby-saml library, which provides SAML single sign-on capabilities for Ruby applications. The root cause is a parser differential between two XML parsers used by ruby-saml: ReXML and Nokogiri. These parsers interpret the same XML input differently, resulting in divergent document object models. This discrepancy can be exploited via a Signature Wrapping attack, where an attacker crafts a malicious SAML response containing multiple XML elements with signatures. The application verifies the signature on one element (parsed by one parser) but processes a different element (parsed by the other parser), effectively bypassing signature verification. This flaw leads to authentication bypass, allowing attackers to impersonate legitimate users without credentials. The vulnerability affects ruby-saml versions before 1.12.4 and versions from 1.13.0 up to but not including 1.18.0. The issue was patched in versions 1.12.4 and 1.18.0. The CVSS v4.0 score is 9.3 (critical), reflecting the network attack vector, no required privileges or user interaction, and high impact on confidentiality and integrity. No known exploits are currently reported in the wild, but the nature of the vulnerability makes it a high-risk target for attackers. The vulnerability is categorized under CWE-347 (Improper Verification of Cryptographic Signature) and CWE-436 (Interpretation Conflict).

For European organizations, the impact of this vulnerability is severe. Many enterprises and government agencies rely on SAML-based SSO for secure authentication across multiple services. Exploitation can lead to unauthorized access to sensitive systems, data exfiltration, and lateral movement within networks. Confidentiality is compromised as attackers can impersonate users and access protected resources. Integrity is affected because the authentication mechanism can be subverted, allowing malicious actors to bypass security controls. Availability is less directly impacted but could be affected if attackers leverage access to disrupt services. The vulnerability's ease of exploitation (no authentication or user interaction required) increases risk. Organizations using vulnerable ruby-saml versions in their identity and access management infrastructure face elevated risks of breaches, regulatory non-compliance (e.g., GDPR), and reputational damage.

1. Immediately upgrade ruby-saml to version 1.12.4 or 1.18.0 or later, which contain patches addressing the parser differential and signature verification issues. 2. Audit all SAML SSO implementations to confirm the use of patched ruby-saml versions and consistent XML parsing libraries. 3. Implement strict XML schema validation and reject SAML assertions containing multiple signature elements or unexpected XML structures. 4. Employ runtime monitoring and anomaly detection on authentication flows to detect unusual SAML responses or authentication bypass attempts. 5. Review and enhance logging around SAML authentication events to enable rapid detection and forensic analysis of suspicious activity. 6. Educate development and security teams on the risks of parser differentials and signature wrapping attacks to prevent similar issues in custom SAML integrations. 7. Consider deploying Web Application Firewalls (WAFs) with rules targeting known signature wrapping attack patterns. 8. Coordinate with identity providers and service providers to ensure end-to-end security of SAML assertions and signatures.