Profile Applicability:
 • Level 2

Description:
The udf kernel module provides support for the Universal Disk Format (UDF) filesystem, commonly used on optical media such as DVDs and Blu-ray discs.

Rationale:
 Disabling the udf kernel module when not required reduces the kernel attack surface by preventing the loading of unnecessary filesystem modules, minimizing potential vulnerabilities.

Impact:
 Pros:

  • Reduces kernel attack surface by disabling unused filesystem support.

  • Helps mitigate risks related to UDF filesystem vulnerabilities.

Cons:

  • Systems needing to mount UDF filesystems will be unable to do so if the module is disabled.

Default Value:
 The udf kernel module may be available and enabled by default on many Linux systems.

Pre-requisites:

  • Root or sudo privileges to modify kernel module configurations.

  • Access to /etc/modprobe.d/ to configure blacklisting or disabling.

Remediation:

Test Plan:

Using Linux command line:

  1. Check if the udf module is loaded:

     lsmod | grep udf

  2. Verify blacklist or disable entries:

    grep -r udf /etc/modprobe.d/

  3. Test module load behavior:

     modprobe -n -v udf

    Expected output should show the module is disabled, e.g., install /bin/false.

Implementation Plan:

Using Linux command line:

  1. Create or edit /etc/modprobe.d/udf.conf:

    echo "install udf /bin/false" > /etc/modprobe.d/udf.conf
 echo "blacklist udf" >> /etc/modprobe.d/udf.conf

  2. Unload the module if currently loaded:

     modprobe -r udf

  3. Reboot the system or reload kernel module configurations.

Backout Plan:

Using Linux command line:

  1. Remove blacklist and disable entries:

    sed -i '/udf/d' /etc/modprobe.d/udf.conf


  2. Optionally reload the module:

    modprobe udf

  3. Reboot the system.

References: