A Vulnerability in OpenSSH Could Allow for Remote Code Execution

A vulnerability has been discovered in OpenSSH that could allow for remote code execution. OpenSSH is a suite of secure networking utilities based on the SSH protocol and is crucial for secure communication over unsecured networks. It is widely used in enterprise environments for remote server management, secure file transfers, and various DevOps practices. Successful exploitation of this vulnerability could allow for remote code execution in the context of the unprivileged user running the sshd server. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

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

A vulnerability has been discovered in OpenSSH, which could allow for remote code execution. Details of the vulnerability include:

Tactic: Initial Access (TA0001):

Technique: Exploit Public-Facing Application (T1190):

• A signal handler race condition vulnerability was found in OpenSSH's server (sshd) where a client does not authenticate within LoginGraceTime seconds (120 by default, 600 in old OpenSSH versions), then sshd's SIGALRM handler is called asynchronously. However, this signal handler calls various functions that are not async-signal-safe, for example, syslog(). This issue leaves it vulnerable to a signal handler race condition on the cleanup_exit() function. ( CVE-2024-6409)

Successful exploitation of this vulnerability could allow for remote code execution in the context of the unprivileged user running the sshd server. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

We recommend the following actions be taken:

• Apply appropriate mitigations provided by OpenSSH or affected Linux vendor 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.