Cis Ubuntu2004 V300 6 3 3 16

6.3.3.16 Ensure successful and unsuccessful attempts to use the setfacl command are collected (Automated)

Profile

• Level 2 - Server
• Level 2 - Workstation

Description

The operating system must generate audit records for successful/unsuccessful uses of the setfacl command

Rationale

This utility sets Access Control Lists (ACLs) of files and directories. Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.

Audit records can be generated from various components within the information system (e.g., module or policy filter).

Audit Procedure

Command Line

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

# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && awk "/^ *-a *always,exit/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -F *auid>=${UID_MIN}/ \
&&/ -F *perm=x/ \
&&/ -F *path=\/usr\/bin\/setfacl/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" /etc/audit/rules.d/*.rules || printf "ERROR: Variable 'UID_MIN' is unset.\n"
}

Verify the output matches:

-a always,exit -F path=/usr/bin/setfacl -F perm=x -F auid>=1000 -F auid!=unset -k perm_chng

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

# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && auditctl -l | awk "/^ *-a *always,exit/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -F *auid>=${UID_MIN}/ \
&&/ -F *perm=x/ \
&&/ -F *path=\/usr\/bin\/setfacl/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"
}

Verify the output matches:

-a always,exit -S all -F path=/usr/bin/setfacl -F perm=x -F auid>=1000 -F auid!=-1 -F key=perm_chng

Expected Result

Both on disk and running configuration should show setfacl audit rules.

Remediation

Command Line

Create audit rules - Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor successful and unsuccessful attempts to use the setfacl command.

Example:

# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && printf "
-a always,exit -F path=/usr/bin/setfacl -F perm=x -F auid>=${UID_MIN} -F auid!=unset -k perm_chng
" >> /etc/audit/rules.d/50-perm_chng.rules || printf "ERROR: Variable 'UID_MIN' is unset.\n"
}

Load audit 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

1. NIST SP 800-53 Rev. 5: AU-2, AU-12, SI-5

CIS Controls

MITRE ATT&CK Mappings: T1562, T1562.006 / TA0005 / M1022