CVE-2025-29774: xml-crypto Auth Bypass Vulnerability

CVE-2025-29774 Overview

CVE-2025-29774 is a critical signature verification bypass vulnerability in xml-crypto, an XML digital signature and encryption library for Node.js. This flaw allows attackers to modify valid signed XML messages in a way that still passes signature verification checks, effectively bypassing authentication or authorization mechanisms in systems relying on xml-crypto for verifying signed XML documents.

The vulnerability is particularly dangerous in SAML-based authentication flows, where XML signatures are used to verify the authenticity of identity assertions. An attacker exploiting this vulnerability could alter critical identity or access control attributes within a signed XML document, enabling privilege escalation or user impersonation attacks against any user with a valid account.

Critical Impact

Attackers can bypass XML signature verification to modify signed documents, enabling privilege escalation and user impersonation in SAML and other XML-based authentication systems.

Affected Products

• xml-crypto versions prior to 6.0.1
• xml-crypto versions prior to 3.2.1 (v3.x branch)
• xml-crypto versions prior to 2.1.6 (v2.x branch)

Discovery Timeline

• 2025-03-14 - CVE-2025-29774 published to NVD
• 2025-03-15 - Last updated in NVD database

Technical Details for CVE-2025-29774

Vulnerability Analysis

This vulnerability is classified under CWE-347 (Improper Verification of Cryptographic Signature), indicating a fundamental flaw in how the xml-crypto library validates XML digital signatures. The issue allows modifications to signed XML content that evade detection during signature verification.

In typical XML signature implementations, the entire referenced content should be canonicalized and hashed, with any modification invalidating the signature. However, the vulnerable versions of xml-crypto contain a flaw in this verification process that permits specific modifications to the signed XML structure while maintaining a valid signature.

This type of vulnerability, often referred to as an XML Signature Wrapping attack variant, exploits weaknesses in how the XML signature verification process handles document structure. The attack is particularly impactful in SAML implementations where signed assertions contain user identity information, roles, and permissions.

Root Cause

The root cause stems from improper verification of cryptographic signatures in the xml-crypto library. The signature validation logic fails to properly bind the signature to all relevant content, allowing attackers to inject or modify elements within the XML document without invalidating the cryptographic signature. This represents a fundamental implementation error in the signature verification workflow that has been addressed in the patched versions through commits to the xml-crypto repository.

Attack Vector

The attack is network-based and requires no user interaction or prior authentication. An attacker with access to a valid signed XML message can craft a modified version that:

1. Preserves the original valid signature
2. Modifies identity attributes (username, email, role)
3. Alters access control permissions or session parameters
4. Passes signature verification on the target system

The modified document can be submitted to any service using vulnerable xml-crypto versions for SAML authentication, API authorization, or other XML-signed message verification. A low-privileged user could escalate to administrator privileges or impersonate other users by manipulating the signed assertions.

For detailed technical analysis of this vulnerability class, see the WorkOS Blog on SAMLStorm and the GitHub Security Advisory GHSA-9p8x-f768-wp2g.

Detection Methods for CVE-2025-29774

Indicators of Compromise

• Unusual privilege escalation events following SAML authentication
• Authentication logs showing users accessing resources outside their normal permissions
• Discrepancies between IDP (Identity Provider) logs and SP (Service Provider) session attributes
• Multiple failed authentication attempts followed by successful access with elevated privileges

Detection Strategies

• Audit all Node.js applications for xml-crypto dependency versions using npm audit or yarn audit
• Implement logging that captures the full SAML assertion content alongside authentication decisions
• Enable correlation between Identity Provider issued assertions and Service Provider accepted claims
• Deploy runtime application security monitoring to detect signature verification anomalies

Monitoring Recommendations

• Monitor authentication events for privilege escalation patterns post-SAML authentication
• Implement anomaly detection for user sessions where accessed resources exceed expected permissions
• Review application dependency manifests regularly for vulnerable xml-crypto versions
• Set up alerts for authentication flows involving users accessing admin or sensitive functions unexpectedly

How to Mitigate CVE-2025-29774

Immediate Actions Required

• Upgrade xml-crypto to version 6.0.1 for applications using the v6.x branch
• Upgrade xml-crypto to version 3.2.1 for applications using the v3.x branch
• Upgrade xml-crypto to version 2.1.6 for applications using the v2.x branch
• Conduct a full security audit of SAML authentication flows in affected applications
• Review access logs for any signs of privilege escalation that may indicate prior exploitation

Patch Information

Security patches have been released across all supported branches of xml-crypto. The fixes are available in the following releases:

• Version 6.0.1 - For applications on the latest v6.x branch
• Version 3.2.1 - For applications on the v3.x branch
• Version 2.1.6 - For applications on the legacy v2.x branch

The security fixes are documented in the GitHub Security Advisory and corresponding commit updates.

Workarounds

• If immediate patching is not possible, consider temporarily disabling SAML authentication in favor of alternative authentication methods
• Implement additional validation layers at the application level to verify user identity attributes match expected values
• Apply network-level restrictions to limit access to SAML endpoints to trusted Identity Providers only
• Consider implementing additional authorization checks that do not rely solely on SAML assertion content

# Update xml-crypto to patched version
npm update xml-crypto

# Or install specific patched version
npm install xml-crypto@6.0.1

# For v3.x applications
npm install xml-crypto@3.2.1

# For v2.x applications
npm install xml-crypto@2.1.6

# Verify installed version
npm list xml-crypto