A recently discovered critical vulnerability, registered as CVE-2025-23369, has been identified in GitHub Enterprise Server. This vulnerability concerns an improper verification of cryptographic signature that, if exploited, would allow signature spoofing for unauthorized internal users. This post aims to shed light on the exploit details, including code snippets and relevant references to help understand and mitigate the issue.

It's important to note that instances of GitHub Enterprise Server not utilizing SAML single sign-on or where the attacker is not already an existing user were not impacted by this vulnerability. The affected versions of GitHub Enterprise Server are those prior to 3.12.14, 3.13.10, 3.14.7, 3.15.2, and 3.16.. This security flaw was responsibly disclosed via the GitHub Bug Bounty program.

For more information about this vulnerability, you can refer to the following resources

- GitHub Security Advisory
- CVE-2025-23369 Details
- National Vulnerability Database (NVD) Entry

Exploit Details

The core issue of this vulnerability lies in the improper verification of cryptographic signatures. Attackers who can exploit this flaw can effectively spoof signatures, allowing unauthorized internal users to perform actions that should have been restricted otherwise.

Below is a simple code snippet demonstrating the issue

def verify_signature(document, signature):
    # Replace this function with a proper cryptographic signature verification
    # This example is for demonstration purposes only
    return True

def sign_document(document, private_key):
    # Replace this function with a proper cryptographic signing
    # This example is for demonstration purposes only
    signature = "signed_with_private_key"
    return signature

document = "Important document"
# Malicious user can replace this signature with one they forge
signature = sign_document(document, "private_key")
if verify_signature(document, signature):
    print("Signature Verified!")
else:
    print("Signature Not Verified!")

In this example, the verify_signature function does not properly validate the signature, which allows the attacker to create a forged signature that would still pass the verification process.

Mitigation

To prevent this vulnerability from being exploited, users are strongly advised to upgrade their GitHub Enterprise Server instances to version 3.12.14, 3.13.10, 3.14.7, 3.15.2, or 3.16., depending on their current major and minor version.

In addition, it is recommended to review the entire codebase for any similar issues and implement proper cryptographic signature verification methods to eliminate the possibility of signature spoofing.

Furthermore, implementing access controls, monitoring, and auditing will help restrict unauthorized access to critical resources, and provide better visibility into potential indicators of compromise.

In conclusion, the discovery of CVE-2025-23369 serves as an important reminder of the potential risks associated with improper cryptographic signature verification. By updating to the latest version of GitHub Enterprise Server and following best practices for secure development, users can help safeguard their systems and protect sensitive information against unauthorized access and exploitation.

Timeline

Published on: 01/21/2025 19:15:12 UTC
Last modified on: 02/05/2025 19:15:45 UTC