CVE-2025-23369: GitHub Enterprise Server Auth Bypass Flaw

CVE-2025-23369 Overview

An improper verification of cryptographic signature vulnerability was identified in GitHub Enterprise Server that allows SAML signature spoofing by unauthorized internal users. This authentication bypass vulnerability enables attackers who already have a valid user account on the system to spoof cryptographic signatures, potentially gaining unauthorized access to other user accounts or elevated privileges within the SAML authentication flow.

The vulnerability specifically impacts instances configured with SAML single sign-on (SSO) authentication. Organizations not utilizing SAML SSO or environments where attackers do not already have an existing user account are not impacted by this vulnerability.

Critical Impact

Existing authenticated users can spoof SAML signatures to impersonate other users or escalate privileges, potentially compromising enterprise source code repositories and CI/CD pipelines.

Affected Products

• GitHub Enterprise Server versions prior to 3.12.14
• GitHub Enterprise Server versions prior to 3.13.10
• GitHub Enterprise Server versions prior to 3.14.7
• GitHub Enterprise Server versions prior to 3.15.2
• GitHub Enterprise Server version 3.16.0 (first patched release in 3.16.x branch)

Discovery Timeline

• 2025-01-21 - CVE-2025-23369 published to NVD
• 2025-09-05 - Last updated in NVD database

This vulnerability was reported via the GitHub Bug Bounty program.

Technical Details for CVE-2025-23369

Vulnerability Analysis

This vulnerability stems from improper verification of cryptographic signatures in the SAML authentication implementation within GitHub Enterprise Server. SAML (Security Assertion Markup Language) relies on cryptographic signatures to ensure the authenticity and integrity of authentication assertions exchanged between identity providers and service providers.

The flaw allows an existing authenticated user to craft or manipulate SAML assertions with spoofed signatures that the GitHub Enterprise Server incorrectly validates as legitimate. This breaks the fundamental trust model of SAML-based authentication, where the service provider should only accept assertions signed by the trusted identity provider.

The network-based attack vector with high attack complexity indicates that while exploitation requires specific conditions to be met—including prior authenticated access and SAML SSO configuration—successful exploitation can result in high confidentiality and integrity impact on the target system.

Root Cause

The root cause is classified as CWE-347: Improper Verification of Cryptographic Signature. The vulnerability exists in the signature validation logic of the SAML authentication handler, which fails to properly verify that cryptographic signatures on SAML assertions are valid and originated from the configured identity provider.

This type of vulnerability typically occurs when:

• Signature validation is not enforced on all critical assertion elements
• The application accepts unsigned or partially signed assertions
• Signature wrapping attacks are not properly mitigated
• The validation logic contains logical flaws that allow bypass conditions

Attack Vector

The attack requires the following conditions:

1. SAML SSO Configuration: The target GitHub Enterprise Server instance must be configured to use SAML single sign-on for authentication
2. Existing User Account: The attacker must already have a valid user account on the GitHub Enterprise Server instance
3. Network Access: The attack is conducted over the network against the SAML authentication endpoints

An attacker with these prerequisites can craft malicious SAML assertions with spoofed signatures. Due to the improper verification in the signature validation logic, the GitHub Enterprise Server accepts these forged assertions as valid, allowing the attacker to authenticate as another user or potentially gain elevated privileges within the system.

The exploitation could enable unauthorized access to private repositories, modification of code, access to secrets and CI/CD configurations, and potential lateral movement within the organization's development infrastructure.

Detection Methods for CVE-2025-23369

Indicators of Compromise

• Unusual SAML authentication events where a user appears to authenticate from unexpected identity provider attributes
• Authentication logs showing session establishment for users without corresponding identity provider audit trail
• Multiple users authenticating with similar or identical SAML assertion patterns in short timeframes
• Unexpected access to private repositories by users who should not have permission

Detection Strategies

• Review GitHub Enterprise Server authentication audit logs for anomalous SAML authentication patterns
• Correlate SAML assertions logged by GitHub Enterprise Server with identity provider audit logs to identify discrepancies
• Monitor for users accessing repositories or organization settings outside their normal access patterns
• Implement alerting on authentication events from users whose last authentication timestamp differs significantly from identity provider records

Monitoring Recommendations

• Enable verbose logging for SAML authentication events in GitHub Enterprise Server
• Configure log forwarding to a SIEM platform for centralized analysis and correlation
• Establish baseline authentication patterns for users and alert on statistical anomalies
• Regularly audit user access permissions and compare against expected role assignments

How to Mitigate CVE-2025-23369

Immediate Actions Required

• Upgrade GitHub Enterprise Server to a patched version immediately: 3.12.14, 3.13.10, 3.14.7, 3.15.2, or 3.16.0 depending on your current version branch
• Review recent authentication logs for any signs of exploitation before patching
• Audit user access and repository permissions for any unauthorized changes
• Consider temporarily disabling SAML SSO and reverting to built-in authentication if immediate patching is not possible

Patch Information

GitHub has released security patches addressing this vulnerability across all supported version branches. Organizations should upgrade to the following minimum versions:

For detailed release information, see the official GitHub documentation:

• GitHub Enterprise Server 3.12.14 Release Notes
• GitHub Enterprise Server 3.13.10 Release Notes
• GitHub Enterprise Server 3.14.7 Release Notes
• GitHub Enterprise Server 3.15.2 Release Notes

Workarounds

• Temporarily disable SAML SSO authentication and use built-in authentication methods until patching is complete
• Implement network-level restrictions to limit access to GitHub Enterprise Server authentication endpoints
• Enable additional logging and monitoring on SAML authentication flows to detect potential exploitation attempts
• Review and restrict user accounts to minimize the potential attack surface from existing users