cyberstrikeus CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 4.1.3
Profile
- Level: 2 - Server
- Level: 2 - Workstation
- Assessment Status: Automated
Description
Capture events where the system date and/or time has been modified. The parameters in this section are set to determine if the adjtimex (tune kernel clock), settimeofday (Set time, using timeval and timezone structures) stime (using seconds since 1/1/1970) or clock_settime (allows for the setting of several internal clocks and timers) system calls have been executed and always write an audit record to the /var/log/audit/audit.log file upon exit, tagging the records with the identifier "time-change".
Note: Reloading the auditd config to set active settings requires the auditd service to be restarted, and may require a system reboot.
Rationale
Unexpected changes in system date and/or time could be a sign of malicious activity on the system.
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 time-change /etc/audit/rules.d/*.rules
Verify the output matches:
-a always,exit -F arch=b32 -S adjtimex -S settimeofday -S stime -k time-change
-a always,exit -F arch=b32 -S clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
Run the following command to verify that rules are in the running auditd config:
auditctl -l | grep time-change
Verify the output matches:
-a always,exit -F arch=b32 -S stime,settimeofday,adjtimex -F key=time-change
-a always,exit -F arch=b32 -S clock_settime -F key=time-change
-w /etc/localtime -p wa -k time-change
On a 64 bit system:
Run the following command to verify the rules are contained in a .rules file in the /etc/audit/rules.d/ directory:
grep time-change /etc/audit/rules.d/*.rules
Verify the output matches:
-a always,exit -F arch=b64 -S adjtimex -S settimeofday -k time-change
-a always,exit -F arch=b32 -S adjtimex -S settimeofday -S stime -k time-change
-a always,exit -F arch=b64 -S clock_settime -k time-change
-a always,exit -F arch=b32 -S clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
Run the following command to verify that rules are in the running auditd config:
auditctl -l | grep time-change
Verify the output matches:
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=time-change
-a always,exit -F arch=b32 -S stime,settimeofday,adjtimex -F key=time-change
-a always,exit -F arch=b64 -S clock_settime -F key=time-change
-a always,exit -F arch=b32 -S clock_settime -F key=time-change
-w /etc/localtime -p wa -k time-change
Expected Result
Output should match the rules listed above for the appropriate architecture.
Remediation
Command Line
For 32 bit systems: Edit or create a file in the /etc/audit/rules.d/ directory ending in .rules.
Example: vi /etc/audit/rules.d/50-time-change.rules
Add the following lines:
-a always,exit -F arch=b32 -S adjtimex -S settimeofday -S stime -k time-change
-a always,exit -F arch=b32 -S clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
For 64 bit systems: Edit or create a file in the /etc/audit/rules.d/ directory ending in .rules.
Example: vi /etc/audit/rules.d/50-time-change.rules
Add the following lines:
-a always,exit -F arch=b64 -S adjtimex -S settimeofday -k time-change
-a always,exit -F arch=b32 -S adjtimex -S settimeofday -S stime -k time-change
-a always,exit -F arch=b64 -S clock_settime -k time-change
-a always,exit -F arch=b32 -S clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
Default Value
By default, no audit rules are configured for time-change events.
References
- CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Section 4.1.3
CIS Controls
| Controls Version | Control |
|---|---|
| v7 | 5.5 Implement Automated Configuration Monitoring Systems - Utilize a Security Content Automation Protocol (SCAP) compliant configuration monitoring system to verify all security configuration elements, catalog approved exceptions, and alert when unauthorized changes occur. |