cis-ubuntu1804-v220-5-2-3-5

5.2.3.5 Ensure events that modify the system's network environment are collected

Profile Applicability

• Level 2 - Server
• Level 2 - Workstation

Description

Record changes to network environment files or system calls. The below parameters monitors the following system calls, and write an audit event on system call exit:

• sethostname - set the systems host name
• setdomainname - set the systems domain name

The files being monitored are:

• /etc/issue and /etc/issue.net - messages displayed pre-login
• /etc/hosts - file containing host names and associated IP addresses
• /etc/networks - symbolic names for networks
• /etc/network/ - directory containing network interface scripts and configurations files

Rationale

Monitoring sethostname and setdomainname will identify potential unauthorized changes to host and domainname of a system. The changing of these names could potentially break security parameters that are set based on those names. The /etc/hosts file is monitored for changes that can indicate an unauthorized intruder is trying to change machine associations with IP addresses and trick users and processes into connecting to unintended machines. Monitoring /etc/issue and /etc/issue.net is important, as intruders could put disinformation into those files and trick users into providing information to the intruder. Monitoring /etc/network is important as it can show if network interfaces or scripts are being modified in a way that can lead to the machine becoming unavailable or compromised. All audit records should have a relevant tag associated with them.

Audit

64 Bit systems

On disk configuration

Run the following commands to check the on disk rules:

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

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

Verify the output matches:

-a always,exit -F arch=b64 -S sethostname,setdomainname -k system-locale
-a always,exit -F arch=b32 -S sethostname,setdomainname -k system-locale
-w /etc/issue -p wa -k system-locale
-w /etc/issue.net -p wa -k system-locale
-w /etc/hosts -p wa -k system-locale
-w /etc/networks -p wa -k system-locale
-w /etc/network/ -p wa -k system-locale

Running configuration

Run the following command to check loaded rules:

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

auditctl -l | awk '/^ *-w/ \
&&(/\/etc\/issue/ \
 ||/\/etc\/issue.net/ \
 ||/\/etc\/hosts/ \
 ||/\/etc\/networks/ \
 ||/\/etc\/network\/ /) \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/'

Verify the output includes:

-a always,exit -F arch=b64 -S sethostname,setdomainname -F key=system-locale
-a always,exit -F arch=b32 -S sethostname,setdomainname -F key=system-locale
-w /etc/issue -p wa -k system-locale
-w /etc/issue.net -p wa -k system-locale
-w /etc/hosts -p wa -k system-locale
-w /etc/networks -p wa -k system-locale
-w /etc/network/ -p wa -k system-locale

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 events that modify the system's network environment.

64 Bit systems

Example:

printf "
-a always,exit -F arch=b64 -S sethostname,setdomainname -k system-locale
-a always,exit -F arch=b32 -S sethostname,setdomainname -k system-locale
-w /etc/issue -p wa -k system-locale
-w /etc/issue.net -p wa -k system-locale
-w /etc/hosts -p wa -k system-locale
-w /etc/networks -p wa -k system-locale
-w /etc/network/ -p wa -k system-locale
" >> /etc/audit/rules.d/50-system_locale.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.

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.