Cis Ubuntu1804 V220 5 2 3 1

5.2.3.1 Ensure changes to system administration scope (sudoers) is collected

Profile Applicability

• Level 2 - Server
• Level 2 - Workstation

Description

Monitor scope changes for system administrators. If the system has been properly configured to force system administrators to log in as themselves first and then use the sudo command to execute privileged commands, it is possible to monitor changes in scope. The file /etc/sudoers, or files in /etc/sudoers.d, will be written to when the file(s) or related attributes have changed. The audit records will be tagged with the identifier "scope".

Rationale

Changes in the /etc/sudoers and /etc/sudoers.d files can indicate that an unauthorized change has been made to the scope of system administrator activity.

Audit

On disk configuration

Run the following command to check the on disk rules:

awk '/^ *-w/ \
&&(/\/etc\/sudoers/ \
 ||/\/etc\/sudoers.d/) \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/' /etc/audit/rules.d/*.rules

Verify the output matches:

-w /etc/sudoers -p wa -k scope
-w /etc/sudoers.d -p wa -k scope

Running configuration

Run the following command to check loaded rules:

auditctl -l | awk '/^ *-w/ \
&&(/\/etc\/sudoers/ \
 ||/\/etc\/sudoers.d/) \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/'

Verify the output matches:

-w /etc/sudoers -p wa -k scope
-w /etc/sudoers.d -p wa -k scope

Remediation

Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor scope changes for system administrators.

Example:

printf "
-w /etc/sudoers -p wa -k scope
-w /etc/sudoers.d -p wa -k scope
" >> /etc/audit/rules.d/50-scope.rules

Merge and load the rules into active configuration:

augenrules --load

Check if reboot is required:

if [[ $(auditctl -s | grep "enabled") =~ "2" ]]; then printf "Reboot required to load rules\n"; fi

References

• NIST SP 800-53 Rev. 5: AU-3

CIS Controls

MITRE ATT&CK Mappings

Additional Information

Potential reboot required: If the auditing configuration is locked (-e 2), then augenrules will not warn in any way that rules could not be loaded into the running configuration. A system reboot will be required to load the rules into the running configuration.

System call structure: For performance (man 7 audit.rules) reasons it is preferable to have all the system calls on one line. However, your configuration may have them on one line each or some other combination.