A Vulnerability in GitHub Enterprise Server (GHES) Could Allow for Authentication Bypass

A vulnerability has been discovered in GitHub Enterprise Server (GHES), which could allow for authentication bypass. GHES is a popular platform for software developers. Organizations can build and store software applications using Git version control and automate deployment pipelines. Successful exploitation of this vulnerability could allow for an attacker to forge a SAML response to provision and/or gain access to a user with site administrator privileges. An attacker could then view, change, or delete data; or create new accounts with full user rights.

There are currently no reports of this vulnerability being exploited in the wild.

A vulnerability has been discovered in GitHub Enterprise Server (GHES), which could allow for authentication bypass. Details of the vulnerability is as follows:
Tactic: Initial Access (TA0001):
Technique: Exploit Public-Facing Application (T1190):

• An authentication bypass vulnerability was present in the GitHub Enterprise Server (GHES) when utilizing SAML single sign-on authentication with the optional encrypted assertions feature. This vulnerability allowed an attacker to forge a SAML response to provision and/or gain access to a user with site administrator privileges. Exploitation of this vulnerability would allow unauthorized access to the instance without requiring prior authentication.
  Successful exploitation of this vulnerability could allow for an attacker to forge a SAML response to provision and/or gain access to a user with site administrator privileges. An attacker could then view, change, or delete data; or create new accounts with full user rights.

We recommend the following actions be taken:

• Apply appropriate updates provided by GitHub to vulnerable systems immediately after appropriate testing. (M1051: Update Software)
• Safeguard 7.1: Establish and Maintain a Vulnerability Management Process: Establish and maintain a documented vulnerability management process for enterprise assets. Review and update documentation annually, or when significant enterprise changes occur that could impact this Safeguard.
• Safeguard 7.4: Perform Automated Application Patch Management: Perform application updates on enterprise assets through automated patch management on a monthly, or more frequent, basis.
• Safeguard 7.6: Perform Automated Vulnerability Scans of Externally-Exposed Enterprise Assets: Perform automated vulnerability scans of externally-exposed enterprise assets using a SCAP-compliant vulnerability scanning tool. Perform scans on a monthly, or more frequent, basis.
• Safeguard 7.7: Remediate Detected Vulnerabilities: Remediate detected vulnerabilities in software through processes and tooling on a monthly, or more frequent, basis, based on the remediation process.
• Apply the Principle of Least Privilege to all systems and services. Run all software as a non-privileged user (one without administrative privileges) to diminish the effects of a successful attack. (M1026: Privileged Account Management)
• Safeguard 4.7: Manage Default Accounts on Enterprise Assets and Software: Manage default accounts on enterprise assets and software, such as root, administrator, and other pre-configured vendor accounts. Example implementations can include: disabling default accounts or making them unusable.
• Safeguard 5.4: Restrict Administrator Privileges to Dedicated Administrator Accounts: Restrict administrator privileges to dedicated administrator accounts on enterprise assets. Conduct general computing activities, such as internet browsing, email, and productivity suite use, from the user’s primary, non-privileged account.
• Prevent access to file shares, remote access to systems, unnecessary services. Mechanisms to limit access may include use of network concentrators, RDP gateways, etc. (M1035: Limit Access to Resource Over Network)
• Use intrusion detection signatures to block traffic at network boundaries. (M1031: Network Intrusion Prevention)
• Safeguard 13.3: Deploy a Network Intrusion Detection Solution: Deploy a network intrusion detection solution on enterprise assets, where appropriate. Example implementations include the use of a Network Intrusion Detection System (NIDS) or equivalent cloud service provider (CSP) service.
• Safeguard 13.8: Deploy a Network Intrusion Prevention Solution: Deploy a network intrusion prevention solution, where appropriate. Example implementations include the use of a Network Intrusion Prevention System (NIPS) or equivalent CSP service.
• Use capabilities to detect and block conditions that may lead to or be indicative of a software exploit occurring. (M1050: Exploit Protection)
• Safeguard 13.10: Performing Application Layer Filtering: Perform application layer filtering. Example implementations include a filtering proxy, application layer firewall, or gateway.