cis-ubuntu1604-v200-4-1-9

name	cis-ubuntu1604-v200-4-1-9
description	Ensure discretionary access control permission modification events are collected
category	cis-logging
version	2.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-16.04","auditd","logging"]
cis_id	4.1.9
cis_benchmark	CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 4.1.9

Profile

• Level: 2 - Server
• Level: 2 - Workstation
• Assessment Status: Automated

Description

Monitor changes to file permissions, attributes, ownership and group. The parameters in this section track changes for system calls that affect file permissions and attributes. The chmod, fchmod and fchmodat system calls affect the permissions associated with a file. The chown, fchown, fchownat and lchown system calls affect owner and group attributes on a file. The setxattr, lsetxattr, fsetxattr (set extended file attributes) and removexattr, lremovexattr, fremovexattr (remove extended file attributes) control extended file attributes. In all cases, an audit record will only be written for non-system user ids (auid >= 1000) and will ignore Daemon events (auid = 4294967295). All audit records will be tagged with the identifier "perm_mod."

Note: Reloading the auditd config to set active settings requires the auditd service to be restarted, and may require a system reboot.

Rationale

Monitoring for changes in file attributes could alert a system administrator to activity that could indicate intruder activity or policy violation.

Impact

None.

Audit Procedure

Command Line

On a 32 bit system:

Run the following command to verify the rules are contained in a .rules file in the /etc/audit/rules.d/ directory:

grep perm_mod /etc/audit/rules.d/*.rules

Verify output matches:

-a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod
-a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

Run the following command to verify that rules are in the running auditd config:

auditctl -l | grep perm_mod

Verify output matches:

-a always,exit -F arch=b32 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=-1 -F key=perm_mod
-a always,exit -F arch=b32 -S lchown,fchown,chown,fchownat -F auid>=1000 -F auid!=-1 -F key=perm_mod
-a always,exit -F arch=b32 -S setxattr,lsetxattr,fsetxattr,removexattr,lremovexattr,fremovexattr -F auid>=1000 -F auid!=-1 -F key=perm_mod

On a 64 bit system: