New critical vulnerability discovered in OpenSSH: remote code execution risk

A new security issue has been identified in OpenSSH versions 8.7 and 8.8, identified as CVE-2024-6409, which could allow remote code execution (RCE) on vulnerable systems. The vulnerability is due to a race condition in the signal handling within the privilege separation process (privsep) and represents a significant risk to the security of affected systems.

Implications of vulnerability

The issue, reported on July 8, 2024 by researchers at Qualys, has attracted considerable concern due to its potential for exploitation. The vulnerability is found in the grace_alarm_handler() function, which improperly calls cleanup_exit() from a signal handler, which is unsafe behavior as it can invoke non-async-signal-safe functions, exposing the system to possible attacks.

Affected systems and patches

Systems running versions 8.7 and 8.8 of OpenSSH are particularly at risk, including those with portable releases. Additionally, some downstream patches, such as Red Hat's openssh-7.6p1-audit.patch, increase the vulnerability by adding additional calls to cleanup_exit(), which can trigger the vulnerability. This makes the problem even more complex and dangerous to manage.

Security Considerations

While the privsep child process, which operates with reduced privileges compared to the parent server process, limits the immediate impact of CVE-2024-6409, the risk of remote code execution persists. The design of the child process is aimed at minimizing damage in case of compromise, but the presence of a race condition in such a critical security context, such as OpenSSH, cannot be underestimated and requires timely interventions to mitigate existing risks.