Profile Applicability:
 • Level 1

Description:
 The noexec mount option prevents execution of binaries on the mounted filesystem. Applying this option to /var/tmp mitigates the risk of running unauthorized or malicious executables from this temporary directory.

Rationale:
 Setting the noexec option on /var/tmp reduces the risk that attackers can execute malicious code from this partition, enhancing overall system security.

Impact:
 Pros:

  • Helps prevent execution of unauthorized binaries or scripts in /var/tmp.

  • Strengthens system defenses against execution-based attacks.

Cons:

  • Some applications may require execution privileges in /var/tmp, which could be affected.

Default Value:
 The noexec option is not usually set on /var/tmp by default and should be explicitly configured.

Pre-requisites:

  • Root or sudo privileges to modify /etc/fstab and remount filesystems.

  • /var/tmp must be mounted as a separate partition.

Remediation:

Test Plan:

Using Linux command line:

  1. Check current mount options for /var/tmp:

     mount | grep /var/tmp


  2. Verify if noexec is present in /etc/fstab for /var/tmp:

     grep /var/tmp /etc/fstab
    Expected output: Mount options for /var/tmp include noexec.

Implementation Plan:

Using Linux command line:

  1. Edit /etc/fstab to add noexec to /var/tmp mount options. Example:
    /dev/<partition>  /var/tmp  ext4  defaults,nodev,nosuid,noexec  0  0

  2. Remount /var/tmp with new options without reboot:

     mount -o remount,noexec /var/tmp

  3. Verify mount options:

     mount | grep /var/tmp


Backout Plan:

Using Linux command line:

  1. Remove noexec from /var/tmp mount options in /etc/fstab.

  2. Remount /var/tmp without noexec:

     mount -o remount /var/tmp

  3. Verify mount options:

     mount | grep /var/tmp


References: