Cis Ubuntu1804 V220 5 2 3 4

5.2.3.4 Ensure events that modify date and time information are collected

Profile Applicability

• Level 2 - Server
• Level 2 - Workstation

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
• clock_settime - allows for the setting of several internal clocks and timers

system calls have been executed. Further, ensure to write an audit record to the configured audit log file upon exit, tagging the records with a unique identifier such as "time-change".

Rationale

Unexpected changes in system date and/or time could be a sign of malicious activity on the system.

Audit

64 Bit systems

On disk configuration

Run the following command to check the on disk rules:

awk '/^ *-a *always,exit/ \
&&/ -F *arch=b(32|64)/ \
&&/ -S/ \
&&(/adjtimex/ \
 ||/settimeofday/ \
 ||/clock_settime/ ) \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/' /etc/audit/rules.d/*.rules

awk '/^ *-w/ \
&&/\/etc\/localtime/ \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/' /etc/audit/rules.d/*.rules

Verify the output matches:

-a always,exit -F arch=b64 -S adjtimex,settimeofday,clock_settime -k time-change
-a always,exit -F arch=b32 -S adjtimex,settimeofday,clock_settime -k time-change
-w /etc/localtime -p wa -k time-change

Running configuration

Run the following command to check loaded rules:

auditctl -l | awk '/^ *-a *always,exit/ \
&&/ -F *arch=b(32|64)/ \
&&/ -S/ \
&&(/adjtimex/ \
 ||/settimeofday/ \
 ||/clock_settime/ ) \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/'

auditctl -l | awk '/^ *-w/ \
&&/\/etc\/localtime/ \
&&/ +-p *wa/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/'

Verify the output includes:

-a always,exit -F arch=b64 -S adjtimex,settimeofday,clock_settime -F key=time-change
-a always,exit -F arch=b32 -S adjtimex,settimeofday,clock_settime -F key=time-change
-w /etc/localtime -p wa -k time-change

32 Bit systems

Follow the same procedures as for 64 bit systems and ignore any entries with b64. In addition, also audit for the stime system call rule. For example:

-a always,exit -F arch=b32 -S adjtimex,settimeofday,clock_settime,stime -k time-change

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 events that modify date and time information.

64 Bit systems

Example:

printf "
-a always,exit -F arch=b64 -S adjtimex,settimeofday,clock_settime -k time-change
-a always,exit -F arch=b32 -S adjtimex,settimeofday,clock_settime -k time-change
-w /etc/localtime -p wa -k time-change
" >> /etc/audit/rules.d/50-time-change.rules

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. In addition, add stime to the system call audit. Example:

-a always,exit -F arch=b32 -S adjtimex,settimeofday,clock_settime,stime -k time-change

References

• NIST SP 800-53 Rev. 5: AU-3, CM-6

CIS Controls

MITRE ATT&CK Mappings

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.