In mid-2024, a significant security vulnerability, now known as CVE-2025-23369, was discovered in GitHub Enterprise Server (“GHES”). This flaw centers on the way cryptographic signatures are verified internally, making it possible for malicious actors inside an organization to spoof signatures and potentially escalate privileges. This article will break down how the bug works, who was affected, and share exclusive code snippets for educational purposes.

What Was the Vulnerability?

The vulnerability could allow internal, already-authenticated users to bypass proper verification of cryptographic signatures in the GitHub Enterprise environment. In plain English, someone with an account but lacking privilege could make it look as though vital actions (like code pushes, reviews, or internal comments) were truly performed by privileged team members. This undermines security audit trails and can enable serious mischief within an enterprise setting.

3.16.

Official GitHub Advisory for CVE-2025-23369
*Note: The exact advisory link will be listed on GitHub's Security Advisories.*

Technical Background

Most critical operations in GitHub Enterprise Server are tracked via cryptographic signatures, which verify the origin and authenticity of changes. Think merge commits, status reports, or sensitive configurations.

This vulnerability arose because some internal signature verifications used improper validation logic. Specifically, when internal users attempted certain GitHub API or web actions, the backend accepted forged signatures if they followed a certain structure — without properly authenticating the SAML single sign-on context.

Illustrative Example

def verify_signature(request, user):
    # Busted Logic: Uses the provided username and skips SSO check
    claimed_signature = request.get('signature')
    claimed_user = request.get('actor')
    if is_valid_signature(claimed_signature, claimed_user.public_key):
        # Misses SSO verification - vulnerable!
        return True
    return False

A proper verification would require cryptographic proof tied directly to the *current authenticated session* and the SAML SSO token, not just any valid key for a known user.

Attacker logs in as a normal user via SAML SSO.

2. Crafts a signed request that claims to originate from an internal admin or other privileged user.
3. Submits the request with a forged cryptographic signature, but without a corresponding SSO context.
4. GHES backend accepts spoofed action because it just checks if the signature matches any known user’s key, not if the user is currently authenticated via SSO.

Example Exploit Request

{
  "actor": "team_admin",
  "action": "approve_pr",
  "signature": "FAKE_OR_STOLEN_SIG",
  "payload": {
    "pr_id": 1234
  }
}

With this, a malicious (but internal!) user could make it appear that a team admin approved a pull request, for instance, by exploiting faulty signature validation logic.

Audit Trail Corruption: Fake actions undermine the source of truth for enterprise codebases.

- Internal Disruption: Malicious internal actors could push harmful code, fake approvals, or sabotage projects.

Not impacted: If your GitHub Enterprise Server does not use SAML SSO, or if the attacker isn’t already an internal user, you’re safe from this specfic bug. External attackers could NOT exploit this directly.

How Was It Found?

This vulnerability was discovered and responsibly reported through the GitHub Bug Bounty program. Researchers found the bug while fuzz-testing SSO and signature interactions.

Review user lists and SAML SSO identity management policies.

Download latest version:
GitHub Enterprise Downloads

Original References

- GitHub Security Advisory (CVE-2025-23369)
- Official GitHub Release Notes
- GitHub Bug Bounty Program

Conclusion

CVE-2025-23369 is a classic case of how even strong cryptography can fall apart without rigorous context verification. If you run GitHub Enterprise Server and rely on SAML SSO, patching and reviewing your internal access controls is critical. As always, keeping systems updated is the best defense.

Stay secure. If you have questions, the GitHub Security Blog and GHES Docs have more details for administrators.


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Timeline

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