1.1.1.1 Ensure mounting of squashfs filesystems is disabled

Information

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. If this filesystem type is not needed, disable it.

Impact:

Disabling squashfs will prevent the use of snap. Snap is a package manager for Linux for installing Snap packages.



'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. When snaps are deployed on versions of Linux, the Ubuntu app store is used as default back-end, but other stores can be enabled as well.

Solution

Edit or create a file in the /etc/modprobe.d/ directory ending in .conf
Example: vi /etc/modprobe.d/squashfs.conf
and add the following line:

install squashfs /bin/true

Run the following command to unload the squashfs module:

# modprobe -r squashfs

See Also

https://workbench.cisecurity.org/files/3682

Item Details

Category: CONFIGURATION MANAGEMENT, IDENTIFICATION AND AUTHENTICATION

References: 800-53|CM-1, 800-53|CM-2, 800-53|CM-6, 800-53|CM-7, 800-53|IA-5, CSCv6|3.1, CSCv7|5.1

Plugin: Unix

Control ID: 89f123ef8d4e4d69b36c631d5c3529bbb3fa0a0c98a02b21c791731e669d6b21