Vulnerability Discussion

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

The UDF filesystem is used to write DVDs and so could assist in data exfiltration, the so-called "sneakernet".

Note that Microsoft Azure uses UDF.

Check

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

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

blacklist udf

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

Fix

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

install udf /bin/false
blacklist udf