| name | cis-ubuntu1804-v220-5-2-3-13 |
| description | Ensure file deletion events by users are collected |
| version | 2.2.0 |
| category | cis-logging |
| tags | ["cis","ubuntu","linux","ubuntu-18.04","auditing","auditd"] |
| author | CIS Benchmarks |
| target | {"platform":"linux","version":"18.04"} |
| severity_boost | {} |
CIS Ubuntu 18.04 - Ensure file deletion events by users are collected (5.2.3.13)
Metadata
- ID: cis-ubuntu1804-v220-5-2-3-13
- Title: Ensure file deletion events by users are collected
- CIS Control: 5.2.3.13
- 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
Monitor the use of system calls associated with the deletion or renaming of files and file attributes. This configuration statement sets up monitoring for:
unlink - remove a fileunlinkat - remove a file attributerename - rename a filerenameat - rename a file attribute system calls and tags them with the identifier "delete"
Rationale
Monitoring these calls from non-privileged users could provide a system administrator with evidence that inappropriate removal of files and file attributes associated with protected files is occurring. While this audit option will look at all events, system administrators will want to look for specific privileged files that are being deleted or altered.
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 *arch=b[2346][24]/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -S/ \
&&/ -F *auid>=${UID_MIN}/ \
&&(/unlink/||/rename/||/unlinkat/||/renameat/) \
&&/ -F *key=delete/ \
&&/ -k *delete/" /etc/audit/rules.d/*.rules \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"
Expected Output:
-a always,exit -F arch=b64 -S unlink,unlinkat,rename,renameat -F auid>=1000 -F auid!=unset -k delete
-a always,exit -F arch=b32 -S unlink,unlinkat,rename,renameat -F auid>=1000 -F auid!=unset -k delete
Running Configuration (64-bit)
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && auditctl -l | awk "/^ *-a *always,exit/ \
&&/ -F *arch=b[2346][24]/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -S/ \
&&/ -F *auid>=${UID_MIN}/ \
&&(/unlink/||/rename/||/unlinkat/||/renameat/) \
&&/ -F *key=delete/ \
&&/ -k *delete/"
Expected Output:
-a always,exit -F arch=b64 -S rename,unlink,unlinkat,renameat -F auid>=1000 -F auid!=-1 -F key=delete
-a always,exit -F arch=b32 -S unlink,rename,unlinkat,renameat -F auid>=1000 -F auid!=-1 -F key=delete
32-bit Systems
Follow the same procedures as for 64 bit systems and ignore any entries with b64.
Remediation
Create Audit Rules
Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor file deletion events by users.
Example:
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && printf "
-a always,exit -F arch=b64 -S rename,unlink,unlinkat,renameat -F auid>=${UID_MIN} -F auid!=unset -k delete
-a always,exit -F arch=b32 -S rename,unlink,unlinkat,renameat -F auid>=${UID_MIN} -F auid!=unset -k delete
" >> /etc/audit/rules.d/50-delete.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-12, SC-7
CIS Controls
- v8: 8.5 Collect Detailed Audit Logs
- v7: 6.2 Activate audit logging
MITRE ATT&CK Mappings
- Techniques: T1562, T1562.006
- Tactics: TA0005
- Mitigations: M1047
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.
