CVE-2024-6387

Name of the Vulnerable Software and Affected Versions OpenSSH versions 8.5p1 through 9.2p1-2+deb12u3

Description An unauthenticated remote attacker can exploit a signal handler race condition in the OpenSSH server (sshd). The issue occurs when a client fails to authenticate within the LoginGraceTime period (defaulting to 120 seconds, or 600 seconds in older versions), triggering the SIGALRM handler asynchronously. This handler calls functions that are not async-signal-safe, such as syslog(), which can lead to the reuse of previously freed memory. This flaw allows a remote attacker to execute arbitrary code with root privileges. The issue is a regression of a previously reported flaw and affects sshd in its default configuration.

Recommendations Upgrade OpenSSH packages to version 1:9.2p1-2+deb12u3 or newer. As a temporary mitigation, restrict access to the sshd service to minimize the risk of exploitation.