Disable Mounting of squashfs
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Description
To configure the system to prevent the squashfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/squashfs.conf
:
install squashfs /bin/true
This effectively prevents usage of this uncommon filesystem.
The squashfs
filesystem type is a compressed read-only Linux
filesystem embedded in small footprint systems (similar to
cramfs
). A squashfs
image can be used without having
to first decompress the image.
Rationale
Removing support for unneeded filesystem types reduces the local attack
surface of the system.
Shell script
The following script can be run on the host to remediate the issue.
#!/bin/bash
# Remediation is applicable only in certain platforms
if [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; then
if LC_ALL=C grep -q -m 1 "^install squashfs" /etc/modprobe.d/squashfs.conf ; then
sed -i 's#^install squashfs.*#install squashfs /bin/false#g' /etc/modprobe.d/squashfs.conf
else
echo -e "\n# Disable per security requirements" >> /etc/modprobe.d/squashfs.conf
echo "install squashfs /bin/false" >> /etc/modprobe.d/squashfs.conf
fi
if ! LC_ALL=C grep -q -m 1 "^blacklist squashfs$" /etc/modprobe.d/squashfs.conf ; then
echo "blacklist squashfs" >> /etc/modprobe.d/squashfs.conf
fi
else
>&2 echo 'Remediation is not applicable, nothing was done'
fi
Ansible playbook
The following playbook can be run with Ansible to remediate the issue.
- name: Ensure kernel module 'squashfs' is disabled
lineinfile:
create: true
dest: /etc/modprobe.d/squashfs.conf
regexp: install\s+squashfs
line: install squashfs /bin/false
when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
tags:
- CCE-83855-7
- NIST-800-171-3.4.6
- NIST-800-53-CM-6(a)
- NIST-800-53-CM-7(a)
- NIST-800-53-CM-7(b)
- disable_strategy
- kernel_module_squashfs_disabled
- low_complexity
- low_severity
- medium_disruption
- reboot_required
- name: Ensure kernel module 'squashfs' is blacklisted
lineinfile:
create: true
dest: /etc/modprobe.d/squashfs.conf
regexp: ^blacklist squashfs$
line: blacklist squashfs
when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
tags:
- CCE-83855-7
- NIST-800-171-3.4.6
- NIST-800-53-CM-6(a)
- NIST-800-53-CM-7(a)
- NIST-800-53-CM-7(b)
- disable_strategy
- kernel_module_squashfs_disabled
- low_complexity
- low_severity
- medium_disruption
- reboot_required