# Cis Ubuntu1804 V220 5 2 3 5 > Ensure events that modify the system's network environment are collected - Skill: `cyberstrikeus/cis-ubuntu1804-v220-5-2-3-5` (Agent Skill) - Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1804-v220-5-2-3-5` - Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1804-v220-5-2-3-5/raw - Safety review: PASS (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/cyberstrikeus/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: ```bash 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: ```bash 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: ```bash 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: ```bash augenrules --load ``` Check if reboot is required: ```bash 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 | Version | Control | IG 1 | IG 2 | IG 3 | | ------- | -------------------------------------------------------- | ---- | ---- | ---- | | v8 | 8.5 Collect Detailed Audit Logs | | ● | ● | | v7 | 5.5 Implement Automated Configuration Monitoring Systems | | ● | ● | ## MITRE ATT&CK Mappings | Techniques / Sub-techniques | Tactics | Mitigations | | --------------------------- | ------- | ----------- | | T1562, T1562.006 | TA0003 | 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.