Vulnerability Discussion
If an unauthorized user obtains access to a private key without a passcode, that user would have unauthorized access to any system where the associated public key has been installed.
Check
Verify the SSH private key files have a passcode.
For each private key stored on the system, use the following command:
$ sudo ssh-keygen -y -f /path/to/file
If the contents of the key are displayed, this is a finding.
Fix
Create a new private and public key pair that uses a passcode with the following command:
$ sudo ssh-keygen -n [passphrase]