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