cyberstrikeus Ensure hfsplus kernel module is not available
Profile
Level 1 - Server, Level 1 - Workstation, Assessment: Automated
Description
The hfsplus filesystem type is a hierarchical filesystem designed to replace hfs that allows you to mount Mac OS filesystems.
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 hfsplus kernel module is not available on the system - OR - has been disabled.
Run the following script to determine if the hfsplus kernel module is available on the system:
#!/usr/bin/env bash
{
l_mod_name="hfsplus" 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 hfsplus kernel module is not available on the system and no further audit steps are required.
Note: Some systems may include the hfsplus 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 hfsplus kernel module is not loaded and not loadable by performing the following:
Run the following command to verify the hfsplus kernel module is not loaded:
# lsmod | grep 'hfsplus'
Nothing should be returned
Run the following command to verify the hfsplus kernel module is not loadable:
# modprobe --showconfig | grep -P -- '\b(install|blacklist)\h+hfsplus\b'
Verify the output includes:
blacklist hfsplus
-AND-
install hfsplus /bin/false
-OR-
install hfsplus /bin/true
Expected Result
blacklist hfsplus
install hfsplus /bin/false
Remediation
Command Line
Run the following commands to unload the hfsplus kernel module:
# modprobe -r hfsplus 2>/dev/null
# rmmod hfsplus 2>/dev/null
Perform the following to disable the hfsplus kernel module:
Create a file ending in .conf with install hfsplus /bin/false in the /etc/modprobe.d/ directory
Example:
# printf '\n%s\n' "install hfsplus /bin/false" >> hfsplus.conf
Create a file ending in .conf with blacklist hfsplus in the /etc/modprobe.d/ directory
Example:
# printf '\n%s\n' "blacklist hfsplus" >> hfsplus.conf
Default Value
Not disabled by default.
References
- NIST SP 800-53 Rev. 5: 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