OpenSSH has launched security updates addressing two vulnerabilities, a man-in-the-middle (MitM) and a denial of service flaw, with one of many flaws launched over a decade in the past.
Qualys found each vulnerabilities and demonstrated their exploitability to OpenSSH’s maintainers.
OpenSSH (Open Safe Shell) is a free, open-source implementation of the SSH (Safe Shell) protocol, which offers encrypted communication for safe distant entry, file transfers, and tunneling over untrusted networks.
It is likely one of the most generally used instruments on the earth, with excessive ranges of adoption throughout Linux and Unix-based (BSD, macOS) programs present in enterprise environments, IT, DevOps, cloud computing, and cybersecurity functions.
The 2 vulnerabilities
The MiTM vulnerability, tracked beneath CVE-2025-26465, was launched in December 2014 with the discharge of OpenSSH 6.8p1, so the difficulty remained undetected for over a decade.
The flaw impacts OpenSSH shoppers when the ‘VerifyHostKeyDNS’ choice is enabled, permitting risk actors to carry out MitM assaults.
“The assault in opposition to the OpenSSH shopper (CVE-2025-26465) succeeds no matter whether or not the VerifyHostKeyDNS choice is ready to “sure” or “ask” (its default is “no”), requires no consumer interplay, and doesn’t rely on the existence of an SSHFP useful resource file (an SSH fingerprint) in DNS,” explains Qualys.
When enabled, resulting from improper error dealing with, an attacker can trick the shopper into accepting a rogue server’s key by forcing an out-of-memory error throughout verification.
By intercepting an SSH connection and presenting a big SSH key with extreme certificates extensions, the attacker can exhaust the shopper’s reminiscence, bypass host verification, and hijack the session to steal credentials, inject instructions, and exfiltrate information.
Though the ‘VerifyHostKeyDNS’ choice is disabled by default in OpenSSH, it was enabled by default on FreeBSD from 2013 till 2023, leaving many programs uncovered to those assaults.
The second vulnerability is CVE-2025-26466, a pre-authentication denial of service flaw launched in OpenSSH 9.5p1, launched in August 2023.
The problem arises from an unrestricted reminiscence allocation throughout the important thing trade, resulting in uncontrolled useful resource consumption.
An attacker can repeatedly ship small 16-byte ping messages, which forces OpenSSH to buffer 256-byte responses with out instant limits.
Throughout the important thing trade, these responses are saved indefinitely, resulting in extreme reminiscence consumption and CPU overload, probably inflicting system crashes.
The repercussions of exploitation of CVE-2025-26466 is probably not as extreme as the primary flaw, however the truth that it is exploitable earlier than authentication maintains a really excessive danger for disruption.
Safety updates launched
The OpenSSH group printed model 9.9p2 earlier at this time, which addresses each vulnerabilities, so everyone seems to be really useful to maneuver to that launch as quickly as potential.
Moreover, it is suggested to disable VerifyHostKeyDNS except completely crucial and depend on guide key fingerprint verification to make sure safe SSH connections.
Concerning the DoS downside, directors are inspired to implement strict connection price limits and monitor SSH site visitors for irregular patterns to cease potential assaults early.
Extra technical particulars concerning the two flaws can be found by Qualys right here.
