Openssh: machine-in-the-middle attack if verifyhostkeydns is enabled

Summary

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. Affected products named by the advisory: Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat Enterprise Linux 9.4 Extended Update Support; Red Hat Discovery 1.14; and 1 more. Affected products named by the advisory: Red Hat OpenShift Container Platform 4.