AlmaLinux OS 9 must disable mounting of squashfs.

Removing support for unneeded filesystem types reduces the local attack surface of the server.

A squashfs compressed filesystem image can be mounted without first decompressing the image.

Note that Snap packages use squashfs.

Verify that AlmaLinux OS 9 disables the ability to load the squashfs kernel module with the following command:

$ grep squashfs /etc/modprobe.conf /etc/modprobe.d/* 

blacklist squashfs

If the command does not return any output, or the line is commented out, and use of squashfs is not documented with the information system security officer (ISSO) as an operational requirement, this is a finding.

To configure the system to prevent the squashfs kernel module from being loaded, create a *.conf file in /etc/modprobe.d/ with the following content:

install squashfs /bin/false blacklist squashfs