cis-ubuntu2004-v300-6-3-3-1

DevOps & Security

Ensure changes to system administration scope (sudoers) is collected

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6.3.3.1 Ensure changes to system administration scope (sudoers) is collected (Automated)

Profile

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 Procedure

Command Line

On disk configuration - Run the following command to check the on disk rules:

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

Verify the output matches:

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

Expected Result

Both on disk and running configuration should show the sudoers watch rules with key "scope".

Remediation

Command Line

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

Controls Version	Control	IG 1	IG 2	IG 3
v8	8.5 Collect Detailed Audit Logs		X	X
v7	4.8 Log and Alert on Changes to Administrative Group Membership		X	X

MITRE ATT&CK Mappings: T1562, T1562.006 / TA0004 / M1047