Vulnerability Discussion

Without verification of the security functions, security functions may not operate correctly and the failure may go unnoticed. Security function is defined as the hardware, software, and/or firmware of the information system responsible for enforcing the system security policy and supporting the isolation of code and data on which the protection is based. Security functionality includes, but is not limited to, establishing system accounts, configuring access authorizations (i.e., permissions, privileges), setting events to be audited, and setting intrusion detection parameters.

Notifications provided by information systems include, for example, electronic alerts to System Administrators, messages to local computer consoles, and/or hardware indications, such as lights.

This requirement applies to the Ubuntu operating system performing security function verification/testing and/or systems and environments that require this functionality.

Check

Verify that the Advanced Intrusion Detection Environment (AIDE) default script used to check file integrity each 30 days or less is unchanged.

Download the original aide-common package in the /tmp directory:

$ cd /tmp; apt download aide-common

Fetch the SHA1 of the original script file:

$ dpkg-deb --fsys-tarfile /tmp/aide-common_*.deb | tar -xO ./usr/share/aide/config/cron.daily/aide | sha1sum
32958374f18871e3f7dda27a58d721f471843e26 -

Compare with the SHA1 of the file in the daily or monthly cron directory:

$ sha1sum /etc/cron.{daily,monthly}/aide 2>/dev/null
32958374f18871e3f7dda27a58d721f471843e26 /etc/cron.daily/aide

If there is no AIDE script file in the cron directories, or the SHA1 value of at least one file in the daily or monthly cron directory does not match the SHA1 of the original, this is a finding.

Fix

The cron file for AIDE is fairly complex as it creates the report. This file is installed with the "aide-common" package, and the default can be restored by copying it from the package:

Download the original package to the /tmp dir:

$ cd /tmp; apt download aide-common

Extract the aide script to its original place:

$ dpkg-deb --fsys-tarfile /tmp/aide-common_*.deb | sudo tar -x ./usr/share/aide/config/cron.daily/aide -C /

Copy it to the cron.daily directory:

$ sudo cp -f /usr/share/aide/config/cron.daily/aide /etc/cron.daily/aide