RHEL 9 must disable mounting of cramfs.

It is detrimental for operating systems to provide, or install by default, functionality exceeding requirements or mission objectives. These unnecessary capabilities or services are often overlooked and therefore may remain unsecured. They increase the risk to the platform by providing additional attack vectors.

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

Compressed ROM/RAM file system (or cramfs) is a read-only file system designed for simplicity and space-efficiency. It is mainly used in embedded and small-footprint systems.

Verify that RHEL 9 disables the ability to load the cramfs kernel module with the following command:

$ grep -r cramfs /etc/modprobe.conf /etc/modprobe.d/* 

install cramfs /bin/false blacklist cramfs

If the command does not return any output or the lines are commented out, and use of cramfs 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 cramfs kernel module from being loaded, add the following lines to the file /etc/modprobe.d/blacklist.conf (or create blacklist.conf if it does not exist):

install cramfs /bin/false blacklist cramfs