CVE-2018-15473

A user enumeration vulnerability flaw was found in OpenSSH, though version 7.7. The vulnerability occurs by not delaying bailout for an invalid authenticated user until after the packet containing the request has been fully parsed. The highest threat from this vulnerability is to data confidentiality.

Mitigation

Configuring your firewall to limit the origin and/or rate of incoming ssh connections (using the netfilter xt_recent module) will limit the impact of this attack, as it requires a new TCP connection for each username tested. This configuration also provides some protection against brute-force attacks on SSH passwords or keys.

See the following article for more information on limiting access to SSHD: <https://access.redhat.com/solutions/8687&gt;