Run the following script to disable the squashfs module: If the module is available in the running kernel: - Create a file with install squashfs /bin/false in the /etc/modprobe.d/ directory - Create a file with blacklist squashfs in the /etc/modprobe.d/ directory - Unload squashfs from the kernel If available in ANY installed kernel: - Create a file with blacklist squashfs in the /etc/modprobe.d/ directory If the kernel module is not available on the system or pre-compiled into the kernel: - No remediation is necessary #!/usr/bin/env bash { l_mname="squashfs" # set module name l_mtype="fs" # set module type l_mpath="/lib/modules/**/kernel/$l_mtype" l_mpname="$(tr '-' '_' <<< "$l_mname")" l_mndir="$(tr '-' '/' <<< "$l_mname")" module_loadable_fix() { # If the module is currently loadable, add "install {MODULE_NAME} /bin/false" to a file in "/etc/modprobe.d" l_loadable="$(modprobe -n -v "$l_mname")" [ "$(wc -l <<< "$l_loadable")" -gt "1" ] && l_loadable="$(grep -P -- "(^h*install|b$l_mname)b" <<< "$l_loadable")" if ! grep -Pq -- '^h*install /bin/(true|false)' <<< "$l_loadable"; then echo -e " - setting module: \"$l_mname\" to be not loadable" echo -e "install $l_mname /bin/false" >> /etc/modprobe.d/"$l_mpname".conf fi } module_loaded_fix() { # If the module is currently loaded, unload the module if lsmod | grep "$l_mname" > /dev/null 2>&1; then echo -e " - unloading module \"$l_mname\"" modprobe -r "$l_mname" fi } module_deny_fix() { # If the module isn't deny listed, denylist the module if ! modprobe --showconfig | grep -Pq -- "^h*blacklisth+$l_mpnameb"; then echo -e " - deny listing \"$l_mname\"" echo -e "blacklist $l_mname" >> /etc/modprobe.d/"$l_mpname".conf fi } # Check if the module exists on the system for l_mdir in $l_mpath; do if [ -d "$l_mdir/$l_mndir" ] && [ -n "$(ls -A $l_mdir/$l_mndir)" ]; then echo -e " - module: \"$l_mname\" exists in \"$l_mdir\" - checking if disabled..." module_deny_fix if [ "$l_mdir" = "/lib/modules/$(uname -r)/kernel/$l_mtype" ]; then module_loadable_fix module_loaded_fix fi else echo -e " - module: \"$l_mname\" doesn't exist in \"$l_mdir\" " fi done echo -e " - remediation of module: \"$l_mname\" complete " } Impact: As Snap packages utilizes squashfs as a compressed filesystem, disabling squashfs will cause Snap packages to fail. Snap application packages of software are self-contained and work across a range of Linux distributions. This is unlike traditional Linux package management approaches, like APT or RPM, which require specifically adapted packages per Linux distribution on an application update and delay therefore application deployment from developers to their software's end-user. Snaps themselves have no dependency on any external store ("App store"), can be obtained from any source and can be therefore used for upstream software deployment.

Name	Audit Name	Plugin	Category
1.1.1.6 Ensure mounting of squashfs filesystems is disabled	CIS Ubuntu Linux 18.04 LTS v2.2.0 L2 Server	Unix	CONFIGURATION MANAGEMENT
1.1.1.6 Ensure mounting of squashfs filesystems is disabled	CIS Ubuntu Linux 18.04 LTS v2.2.0 L2 Workstation	Unix	CONFIGURATION MANAGEMENT

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