Vulnerability Discussion

SSH provides several logging levels with varying amounts of verbosity. "DEBUG" is specifically not recommended other than strictly for debugging SSH communications since it provides so much data that it is difficult to identify important security information. "INFO" or "VERBOSE" level is the basic level that only records login activity of SSH users. In many situations, such as Incident Response, it is important to determine when a particular user was active on a system. The logout record can eliminate those users who disconnected, which helps narrow the field.

Check

Verify that RHEL 9 logs SSH connection attempts and failures to the server.

Check what the SSH daemon's "LogLevel" option is set to 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*loglevel'

LogLevel VERBOSE

If a value of "VERBOSE" is not returned or the line is commented out or missing, this is a finding.

Fix

Configure RHEL 9 to log connection attempts add or modify the following line in "/etc/ssh/sshd_config".

LogLevel VERBOSE

Restart the SSH daemon for the settings to take effect:

$ sudo systemctl restart sshd.service