A signal handler race condition vulnerability was found in OpenSSH's server (sshd) in Red Hat Enterprise Linux 9, 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, which introduces the same vulnerability as CVE-2024-6387 in the unprivileged child of the SSHD server. As a consequence of a successful attack, in the worst case scenario, the attacker may be able to perform a remote code execution (RCE) within unprivileged user running the sshd server. This vulnerability affects only the sshd server shipped with Red Hat Enterprise Linux 9, while upstream versions of sshd are not impact by this flaw.

A race condition vulnerability was discovered in how signals are handled by OpenSSH's server (sshd). If a remote attacker does not authenticate within a set time period, then sshd's SIGALRM handler is called asynchronously. However, this signal handler calls various functions that are not async-signal-safe, for example, syslog(). As a consequence of a successful attack, in the worst case scenario, an attacker may be able to perform a remote code execution (RCE) as an unprivileged user running the sshd server.

Red Hat, Inc. https://access.redhat.com/errata/RHSA-2024:4457 [No types assigned]