Executive Summary

CVE-2024-6409 exposes a race condition in OpenSSH's sshd SIGALRM handler. When an unauthenticated connection times out, the asynchronous handler invokes non‑async‑signal‑safe functions such as syslog, potentially allowing a remote attacker to execute code as the sshd user. The flaw is triggered by a timeout, not requiring authentication, and currently has no KEV listing.

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Authoritative CVE Metadata - CVSS Base Score: 7.0 (HIGH) - Published: 2024-07-08T18:15:09.487 - Last Modified: 2026-08-21T13:16:25.010

Original Description: 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.

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