Vulnerability Discussion
SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.
Check
Verify the SSH daemon does not allow rhosts authentication with the following command:
$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*ignorerhosts'
IgnoreRhosts yes
If the value is returned as "no", the returned line is commented out, or no output is returned, this is a finding.
Fix
Configure the SSH daemon to not allow rhosts authentication.
Add the following line in "/etc/ssh/sshd_config", or uncomment the line and set the value to "yes":
IgnoreRhosts yes
The SSH service must be restarted for changes to take effect:
$ sudo systemctl restart sshd.service