CVE-2025-26465 — Openssh: machine-in-the-middle attack if verifyhostkeydns is enabled

Affected: OpenSSH, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux 9.4 Extended Update Support, Red Hat Discovery 1.14, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat OpenShift Container Platform 4, Siemens SIDIS Secured SmartPlug and 3 more

A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key. For an attack to be considered successful, the attacker needs to manage to exhaust the client's memory resource first, turning the attack complexity high.

USN-7270-1 — openssh vulnerabilities

Affected: Ubuntu:20.04:LTS: openssh, Ubuntu:22.04:LTS: openssh, Ubuntu:24.04:LTS: openssh

It was discovered that the OpenSSH client incorrectly handled the non-default VerifyHostKeyDNS option. If that option were enabled, an attacker could possibly impersonate a server by completely bypassing the server identity check. (CVE-2025-26465)

It was discovered that OpenSSH incorrectly handled the transport-level ping facility. A remote attacker could possibly use this issue to cause OpenSSH clients and servers to consume resources, leading to a denial of service. This issue only affected Ubuntu 24.04 LTS and Ubuntu 24.10. (CVE-2025-26466)

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CVE-2025-26465 — Openssh: machine-in-the-middle attack if verifyhostkeydns is enabled

USN-7270-1 — openssh vulnerabilities