# Cis Ubuntu2004 V300 6 3 3 5

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

- Skill: `cyberstrikeus/cis-ubuntu2004-v300-6-3-3-5` (Agent Skill)
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- Category: Coding & Dev Tools
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-ubuntu2004-v300-6-3-3-5

---


# 6.3.3.5 Ensure events that modify the system's network environment are collected (Automated)

## Profile

- 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
- `/etc/netplan/` - central location for YAML networking configurations files

## Rationale

Monitoring system events that change network environments, such as `sethostname` and `setdomainname`, helps identify unauthorized alterations to host and domain names, which could compromise security settings reliant on these names. Changes to `/etc/hosts` can signal unauthorized attempts to alter machine associations with IP addresses, potentially redirecting users and processes to unintended destinations. Surveillance of `/etc/issue` and `/etc/issue.net` is crucial to detect intruders inserting false information to deceive users. Monitoring `/etc/network/` reveals modifications to network interfaces or scripts that may jeopardize system availability or security. Additionally, tracking changes in the `/etc/netplan/` directory ensures swift detection of unauthorized adjustments to network configurations. All audit records should be appropriately tagged for relevance.

## Audit Procedure

### Command Line

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\/network \
  ||/\/etc\/netplan) \
&&/ +-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
-w /etc/netplan -p wa -k system-locale
```

## Expected Result

Both on disk and running configuration should show network environment audit rules.

## Remediation

### Command Line

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.

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
-w /etc/netplan -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
```

## References

1. NIST SP 800-53 Rev. 5: AU-3, CM-6
2. https://netplan.io/faq

## CIS Controls

| Controls Version | Control                                                  | IG 1 | IG 2 | IG 3 |
| ---------------- | -------------------------------------------------------- | ---- | ---- | ---- |
| v8               | 8.5 Collect Detailed Audit Logs                          |      | X    | X    |
| v7               | 5.5 Implement Automated Configuration Monitoring Systems |      | X    | X    |

MITRE ATT&CK Mappings: T1562, T1562.006 / TA0003 / M1047