Vulnerability Discussion

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.

Check

Verify the operating system disables the ability to load the cramfs kernel module.

$ sudo grep -ri cramfs /etc/modprobe.d/* | grep -i "/bin/false"
install cramfs /bin/false

If the command does not return any output, or the line is commented out, and use of the cramfs protocol is not documented with the Information System Security Officer (ISSO) as an operational requirement, this is a finding.

Verify the operating system disables the ability to use the cramfs kernel module.

Determine if the cramfs kernel module is disabled with the following command:

$ sudo grep -ri cramfs /etc/modprobe.d/* | grep -i "blacklist"
blacklist cramfs

If the command does not return any output or the output is not "blacklist cramfs", and use of the cramfs kernel module is not documented with the ISSO as an operational requirement, this is a finding.

Fix

Configure the operating system to disable the ability to use the cramfs kernel module.

Add or update the following lines in the file "/etc/modprobe.d/blacklist.conf":

install cramfs /bin/false
blacklist cramfs

Reboot the system for the settings to take effect.