Vulnerability Discussion

Reconstruction of harmful events or forensic analysis is not possible if audit records do not contain enough information.

At a minimum, the organization must audit the full-text recording of privileged ssh commands. The organization must maintain audit trails in sufficient detail to reconstruct events to determine the cause and impact of compromise.

When a user logs on, the auid is set to the uid of the account that is being authenticated. Daemons are not user sessions and have the loginuid set to -1. The auid representation is an unsigned 32-bit integer, which equals 4294967295. The audit system interprets -1, 4294967295, and "unset" in the same way.

Satisfies: SRG-OS-000042-GPOS-00020, SRG-OS-000392-GPOS-00172, SRG-OS-000471-GPOS-00215

Check

Verify the operating system generates audit records when successful/unsuccessful attempts to use the "ssh-keysign" command occur.

Check that the following system call is being audited by performing the following command to check the file system rules in "/etc/audit/audit.rules":

# grep -iw /usr/libexec/openssh/ssh-keysign /etc/audit/audit.rules

-a always,exit -F path=/usr/libexec/openssh/ssh-keysign -F auid>=1000 -F auid!=unset -k privileged-ssh

If the command does not return any output, this is a finding.

Fix

Configure the operating system to generate audit records when successful/unsuccessful attempts to use the "ssh-keysign" command occur.

Add or update the following rule in "/etc/audit/rules.d/audit.rules":

-a always,exit -F path=/usr/libexec/openssh/ssh-keysign -F auid>=1000 -F auid!=unset -k privileged-ssh

The audit daemon must be restarted for the changes to take effect.