1.1.1.7 Ensure squashfs kernel module is not available

Information

The squashfs filesystem type is a compressed read-only Linux filesystem embedded in small footprint systems. A squashfs image can be used without having to first decompress the image.

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

Solution

Unload and disable the squashfs kernel module.

- Run the following commands to unload the squashfs kernel module:

# modprobe -r squashfs 2>/dev/null
# rmmod squashfs 2>/dev/null <xhtml:ol start="2"> - Perform the following to disable the squashfs kernel module:

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

Example:

# printf '%s\n' "" "install squashfs /bin/false" >> /etc/modprobe.d/60-squashfs.conf

Create a file ending inconf with blacklist squashfs in the /etc/modprobe.d/ directory.

Example:

# printf '%s\n' "" "blacklist squashfs" >> /etc/modprobe.d/60-squashfs.conf

Impact:

As Snap packages utilize 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.

See Also

https://workbench.cisecurity.org/benchmarks/23600

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6, 800-53|CM-7, CSCv7|9.2

Plugin: Unix

Control ID: e5e554dd04d702f99d167dd936625d2fdc19a2559d099a49b0779e50cb5a3dcb