cis-ubuntu2004-v300-1-1-1-2

DevOps & Security

Ensure freevxfs kernel module is not available

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_20.04_LTS_Benchmark_v3.0.0/cis-ubuntu2004-v300-1-1-1-2/SKILL.md

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Ensure freevxfs kernel module is not available

Profile

Level 1 - Server, Level 1 - Workstation, Assessment: Automated

Description

The freevxfs filesystem type is a free version of the Veritas type filesystem. This is the primary filesystem type for HP-UX operating systems.

Rationale

Removing support for unneeded filesystem types reduces the local attack surface of the system. If this filesystem type is not needed, disable it.

Audit Procedure

Command Line

Verify the freevxfs kernel module is not available on the system - OR - has been disabled.

Run the following script to determine if the freevxfs kernel module is available on the system:

#!/usr/bin/env bash

{
   l_mod_name="freevxfs" l_mod_type="fs"
   while IFS= read -r l_mod_path; do
      if [ -d "$l_mod_path/${l_mod_name}/-/\/" ] &&  [ -n "$(ls -A "$l_mod_path/${l_mod_name}/-/\/")" ]; then
         printf '%s\n' "$l_mod_name exists in $l_mod_path"
      fi
   done < <(readlink -f /usr/lib/modules/**/kernel/$l_mod_type || readlink -f /lib/modules/**/kernel/$l_mod_type)
}

If nothing is returned, the freevxfs kernel module is not available on the system and no further audit steps are required.

Note: Some systems may include the freevxfs filesystem as part of the kernel opposed to being available as a kernel module. In this case, the above audit will not return anything. This is also considered a passing state.

If anything is returned, verify the freevxfs kernel module is not loaded and not loadable by performing the following:

Run the following command to verify the freevxfs kernel module is not loaded:

# lsmod | grep 'freevxfs'

Nothing should be returned

Run the following command to verify the freevxfs kernel module is not loadable:

# modprobe --showconfig | grep -P -- '\b(install|blacklist)\h+freevxfs\b'

Verify the output includes:

blacklist freevxfs
 -AND-
install freevxfs /bin/false
 -OR-
install freevxfs /bin/true

Expected Result

blacklist freevxfs
install freevxfs /bin/false

Remediation

Command Line

Run the following to unload and disable the freevxfs kernel module:

# modprobe -r freevxfs 2>/dev/null
# rmmod freevxfs 2>/dev/null

Perform the following to disable the freevxfs kernel module:

Create a file ending in .conf with install freevxfs /bin/false in the /etc/modprobe.d/ directory

Example:

# printf '\n%s\n' "install freevxfs /bin/false" >> freevxfs.conf

Create a file ending in .conf with blacklist freevxfs in the /etc/modprobe.d/ directory

Example:

# printf '\n%s\n' "blacklist freevxfs" >> freevxfs.conf

Default Value

Not disabled by default.

References

NIST SP 800-53: CM-7 a
NIST SP 800-53A: CM-7.1 (ii)

CIS Controls

v8 - 4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software (IG 2, IG 3) v7 - 9.2 Ensure Only Approved Ports, Protocols and Services Are Running (IG 2, IG 3)

MITRE ATT&CK Mappings: T1005, T1005.000 | TA0005 | M1050