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

DevOps & Security

Ensure events that modify the sudo log file are collected

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6.3.3.3 Ensure events that modify the sudo log file are collected (Automated)

Profile

Level 2 - Server
Level 2 - Workstation

Description

Monitor the sudo log file. If the system has been properly configured to disable the use of the su command and force all administrators to have to log in first and then use sudo to execute privileged commands, then all administrator commands will be logged to /var/log/sudo.log. Any time a command is executed, an audit event will be triggered as the /var/log/sudo.log file will be opened for write and the executed administration command will be written to the log.

Rationale

Changes in /var/log/sudo.log indicate that an administrator has executed a command or the log file itself has been tampered with. Administrators will want to correlate the events written to the audit trail with the records written to /var/log/sudo.log to verify if unauthorized commands have been executed.

Audit Procedure

Command Line

Note: This recommendation requires that the sudo logfile is configured. See guidance provided in the recommendation "Ensure sudo log file exists".

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

# {
SUDO_LOG_FILE=$(grep -r logfile /etc/sudoers* | sed -e 's/.*logfile=//;s/,? .*//' -e 's/"//g' -e 's|/|\\\/|g')
[ -n "${SUDO_LOG_FILE}" ] && awk "/^ *-w/ \
&&/"${SUDO_LOG_FILE}"/ \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" /etc/audit/rules.d/*.rules \
|| printf "ERROR: Variable 'SUDO_LOG_FILE' is unset.\n"
}

Verify output of matches:

-w /var/log/sudo.log -p wa -k sudo_log_file

Running configuration - Run the following command to check loaded rules:

# {
SUDO_LOG_FILE=$(grep -r logfile /etc/sudoers* | sed -e 's/.*logfile=//;s/,? .*//' -e 's/"//g' -e 's|/|\\\/|g')
[ -n "${SUDO_LOG_FILE}" ] && auditctl -l | awk "/^ *-w/ \
&&/"${SUDO_LOG_FILE}"/ \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" \
|| printf "ERROR: Variable 'SUDO_LOG_FILE' is unset.\n"
}

Verify output matches:

-w /var/log/sudo.log -p wa -k sudo_log_file

Expected Result

Both on disk and running configuration should show a watch rule on the sudo log file.

Remediation

Command Line

Note: This recommendation requires that the sudo logfile is configured. See guidance provided in the recommendation "Ensure sudo log file exists".

Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor events that modify the sudo log file.

Example:

# {
SUDO_LOG_FILE=$(grep -r logfile /etc/sudoers* | sed -e 's/.*logfile=//;s/,? .*//' -e 's/"//g')
[ -n "${SUDO_LOG_FILE}" ] && printf "
-w ${SUDO_LOG_FILE} -p wa -k sudo_log_file
" >> /etc/audit/rules.d/50-sudo.rules || printf "ERROR: Variable 'SUDO_LOG_FILE' is unset.\n"
}

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	4.9 Log and Alert on Unsuccessful Administrative Account Login		X	X

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