cis-ubuntu2004-v300-1-1-2-5-1

name	cis-ubuntu2004-v300-1-1-2-5-1
description	Ensure separate partition exists for /var/tmp
category	cis-storage
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","partition"]
cis_id	1.1.2.5.1
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

Ensure separate partition exists for /var/tmp

Profile

Level 2 - Server, Level 2 - Workstation, Assessment: Automated

Description

The /var/tmp directory is a world-writable directory used for temporary storage by all users and some applications. Temporary files residing in /var/tmp are to be preserved between reboots.

Rationale

The default installation only creates a single / partition. Since the /var/tmp directory is world-writable, there is a risk of resource exhaustion. In addition, other operations on the system could fill up the disk unrelated to /var/tmp and cause potential disruption to daemons as the disk is full.

Configuring /var/tmp as its own file system allows an administrator to set additional mount options such as noexec/nosuid/nodev. These options limit an attacker's ability to create exploits on the system.

Impact

Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem partitions may prevent successful resizing or may require the installation of additional tools solely for the purpose of resizing operations. The use of these additional tools may introduce their own security considerations.

Audit Procedure

Command Line

Run the following command and verify output shows /var/tmp is mounted. Example:

# findmnt -kn /var/tmp

Example output:

/var/tmp   /dev/sdb ext4   rw,nosuid,nodev,noexec,relatime,seclabel

Expected Result

/var/tmp should be mounted as a separate partition.

Remediation

Command Line

For new installations, during installation create a custom partition setup and specify a separate partition for /var/tmp. For systems that were previously installed, create a new partition and configure /etc/fstab as appropriate.

Default Value

Not configured by default.

Additional Information

When modifying /var/tmp it is advisable to bring the system to emergency mode (so auditd is not running), rename the existing directory, mount the new file system, and migrate the data over before returning to multi-user mode.

References

1. AJ Lewis, "LVM HOWTO", http://tldp.org/HOWTO/LVM-HOWTO/