CVE-2025-26466

CVE-2025-26466 is a denial-of-service flaw in the OpenSSH server: for every ping packet the SSH server receives, it allocates a corresponding pong packet in a memory buffer and adds it to a queue, and that memory is only freed once the server/client key exchange completes. A remote, unauthenticated attacker can hold a connection open and keep flooding it with ping packets faster than the key exchange finishes, driving uncontrolled memory growth until the SSH server becomes unavailable. The impact is availability-only, with no code execution or data exposure (CVSS 3.1 score 5.9, network vector with high attack complexity). Any system running an affected OpenSSH build is exposed, notably as packaged in Ubuntu Linux and Debian Linux, with internet-facing SSH endpoints the most attractive targets. No public PoC or confirmed in-the-wild exploitation is known and it is not in CISA KEV, but EPSS of ~40% (99th percentile) signals an elevated probability of exploitation within 30 days; the related headlines describing critical OpenSSH flaws also cover companion issues (including a man-in-the-middle bug) from the same disclosure.

What to do: Install the OpenSSH security updates released by Canonical and Debian in February 2025 (upstream fix in OpenSSH 9.9p2) and verify the running version with 'ssh -V' or your package manager. Until patched, reduce exposure by restricting SSH to trusted sources via firewall allowlists and rate-limiting unauthenticated connections (e.g., MaxStartups or fail2ban), and monitor sshd memory usage for abnormal growth.