Detections
Analytics
1.1.1.7 Ensure mounting of udf filesystems is disabled
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 module:If the module is available in the running kernel:
- Create a file with install udf /bin/false in the /etc/modprobe.d/ directory
- Create a file with blacklist udf in the /etc/modprobe.d/ directory
- Unload udf from the kernel
If available in ANY installed kernel:
- Create a file with blacklist udf in the /etc/modprobe.d/ directory
If the kernel module is not available on the system or pre-compiled into the kernel:
- No remediation is necessary
#!/usr/bin/env bash
{
l_mname="udf" # set module name
l_mtype="fs" # set module type
l_mpath="/lib/modules/**/kernel/$l_mtype"
l_mpname="$(tr '-' '_' <<< "$l_mname")"
l_mndir="$(tr '-' '/' <<< "$l_mname")"
module_loadable_fix()
{
# If the module is currently loadable, add "install {MODULE_NAME} /bin/false" to a file in "/etc/modprobe.d"
l_loadable="$(modprobe -n -v "$l_mname")"
[ "$(wc -l <<< "$l_loadable")" -gt "1" ] && l_loadable="$(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_mpname".conf
fi
}
module_loaded_fix()
{
# If the module is currently loaded, unload the module
if lsmod | grep "$l_mname" > /dev/null 2>&1; then
echo -e "
- unloading module \"$l_mname\""
modprobe -r "$l_mname"
fi
}
module_deny_fix()
{
# If the module isn't deny listed, denylist the module
if ! modprobe --showconfig | grep -Pq -- "^h*blacklisth+$l_mpnameb"; then
echo -e "
- deny listing \"$l_mname\""
echo -e "blacklist $l_mname" >> /etc/modprobe.d/"$l_mpname".conf
fi
}
# Check if the module exists on the system
for l_mdir in $l_mpath; do
if [ -d "$l_mdir/$l_mndir" ] && [ -n "$(ls -A $l_mdir/$l_mndir)" ]; then
echo -e "
- module: \"$l_mname\" exists in \"$l_mdir\"
- checking if disabled..."
module_deny_fix
if [ "$l_mdir" = "/lib/modules/$(uname -r)/kernel/$l_mtype" ]; then
module_loadable_fix
module_loaded_fix
fi
else
echo -e "
- module: \"$l_mname\" doesn't exist in \"$l_mdir\"
"
fi
done
echo -e "
- remediation of module: \"$l_mname\" complete
"
}
Impact:
Microsoft Azure requires the usage of udf
udf should not be disabled on systems run on Microsoft Azure.
See Also
Item Details
Audit Name: CIS Ubuntu Linux 18.04 LTS v2.2.0 L2 Server
Category: CONFIGURATION MANAGEMENT
References: 800-53|CM-6, 800-53|CM-7, CSCv7|9.2
Plugin: Unix
Control ID: 6d09ae1a84e8a1226cb4e7660d03f393e0ec3f6a79c793e032cf7e3b06778504