FORTINET Security Advisory
Published Date: March 11, 2025 (Revised May 25, 2026)
CVE: CVE-2025-26466
Advisory Summary
❗️ Security Alert: Pre-authentication Denial of Service Vulnerability in OpenSSH (CVE-2025-26466)
Fortinet has identified a significant pre-authentication Denial of Service (DoS) vulnerability in the OpenSSH package, tracked as CVE-2025-26466, with a CVSSv3 severity score of 5.9. The flaw involves the handling of ping packets by the SSH server: for every ping received, the server allocates a pong reply in a memory buffer and queues it, only releasing this memory after completing the server/client key exchange.
A malicious actor can exploit this by continuously sending ping packets, leading to an unchecked memory buffer buildup on the server side. This results in excessive memory consumption that can render the SSH server unavailable, effectively causing a denial of service condition without requiring authentication.
Networking and security teams managing OpenSSH deployments should prioritize patching this vulnerability and consider monitoring incoming SSH traffic for anomalous patterns indicative of exploitation attempts. This issue underscores the need for vigilance in protecting critical infrastructure components like SSH services against resource exhaustion attacks.
- Vulnerability affects OpenSSH server memory management during key exchange.
- Exploitable pre-authentication DoS attack vector.
- CVSSv3 score: 5.9 (Medium severity).
- Timely patching and traffic monitoring recommended.
-26466
Reference: Vendor Advisory