1.1.1.2 Ensure mounting of udf filesystems is disabled

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Information

The udf filesystem type is the universal disk format used to implement ISO/IEC 13346 and ECMA-167 specifications. This is an open vendor filesystem type for data storage on a broad range of media. This filesystem type is necessary to support writing DVDs and newer optical disc formats.

Removing support for unneeded filesystem types reduces the local attack surface of the system. If this filesystem type is not needed, disable it.

Solution

Run the following script to disable the udf filesystem:

#!/usr/bin/env bash

{
l_mname="udf" # set module name
# Check if the module exists on the system
if [ -z "$(modprobe -n -v "$l_mname" 2>&1 | grep -Pi -- "h*modprobe:h+FATAL:h+Moduleh+$l_mnameh+noth+foundh+inh+directory")" ]; then
# Remediate loadable
l_loadable="$(modprobe -n -v "$l_mname")"
[ "$(wc -l <<< "$l_loadable")" -gt "1" ] &amp;&amp; l_loadable="$(grep -P -- "(^h*install|b$l_mname)b" <<< "$l_loadable")"
if ! grep -Pq -- '^h*install /bin/(true|false)' <<< "$l_loadable"; then
echo -e " - setting module: \"$l_mname\" to be not loadable"
echo -e "install $l_mname /bin/false" >> /etc/modprobe.d/"$l_mname".conf
fi
# Remediate loaded
if lsmod | grep "$l_mname" > /dev/null 2>&amp;1; then
echo -e " - unloading module \"$l_mname\""
modprobe -r "$l_mname"
fi
# Remediate deny list
if ! modprobe --showconfig | grep -Pq -- "^h*blacklisth+$l_mnameb"; then
echo -e " - deny listing \"$l_mname\""
echo -e "blacklist $l_mname" >> /etc/modprobe.d/"$l_mname".conf
fi
else
echo -e " - Nothing to remediate
- Module \"$l_mname\" doesn't exist on the system"
fi
}

Impact:

Microsoft Azure requires the usage of udf

udf should not be disabled on systems run on Microsoft Azure.

See Also

https://workbench.cisecurity.org/files/4230