cyberstrikeus CIS Ubuntu 18.04 - Ensure successful and unsuccessful attempts to use the setfacl command are recorded (5.2.3.16)
Metadata
- ID: cis-ubuntu1804-v220-5-2-3-16
- Title: Ensure successful and unsuccessful attempts to use the setfacl command are recorded
- CIS Control: 5.2.3.16
- Profile Applicability: Level 2 - Server, Level 2 - Workstation
- Benchmark: CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0
- Category: cis-logging
- Tags: cis, ubuntu, linux, ubuntu-18.04, auditing, auditd
- Severity: medium
- Version: 2.2.0
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).
Impact
None
Audit
On Disk Configuration (64-bit)
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 *[!-~]* *$/)/" /etc/audit/rules.d/*.rules || printf "ERROR: Variable 'UID_MIN' is unset.\n"
Expected Output:
-a always,exit -F path=/usr/bin/setfacl -F perm=x -F auid>=1000 -F auid!=unset -k perm_chng
Running Configuration (64-bit)
UID_MIN=$(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 *[!-~]* *$/)/"
Expected Output:
-a always,exit -S all -F path=/usr/bin/setfacl -F perm=x -F auid>=1000 -F auid!=-1 -F key=perm_chng
32-bit Systems
Follow the same procedures as for 64 bit systems and ignore any entries with b64.
Remediation
Create Audit Rules
Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor successful and unsuccessful attempts to use the setfacl command.
Example:
UID_MIN=$(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
32-bit Systems
Follow the same procedures as for 64 bit systems and ignore any entries with b64.
References
- NIST SP 800-53 Rev. 5: AU-2, AU-12, SI-5
CIS Controls
- v8: 8.2 Collect Audit Logs
- v7: 6.2 Activate audit logging
MITRE ATT&CK Mappings
- Techniques: T1562, T1562.006
- Tactics: TA0005
- Mitigations: M1022
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. This is important to understand for both the auditing and remediation sections as the examples given are optimized for performance as per the man page.