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

name	cis-ubuntu2004-v300-1-1-2-2-1
description	Ensure /dev/shm is a separate partition
category	cis-storage
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","partition"]
cis_id	1.1.2.2.1
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

Ensure /dev/shm is a separate partition

Profile

Level 1 - Server, Level 1 - Workstation, Assessment: Automated

Description

The /dev/shm directory is a world-writable directory that can function as shared memory that facilitates inter process communication (IPC).

Rationale

Making /dev/shm its own file system allows an administrator to set additional mount options such as the noexec option on the mount, making /dev/shm useless for an attacker to install executable code. It would also prevent an attacker from establishing a hard link to a system setuid program and wait for it to be updated. Once the program was updated, the hard link would be broken and the attacker would have his own copy of the program. If the program happened to have a security vulnerability, the attacker could continue to exploit the known flaw.

This can be accomplished by mounting tmpfs to /dev/shm.

Impact

Since the /dev/shm directory is intended to be world-writable, there is a risk of resource exhaustion if it is not bound to a separate partition.

/dev/shm utilizing tmpfs can be resized using the size={size} parameter in the relevant entry in /etc/fstab.

Audit Procedure

Command Line

• IF - /dev/shm is to be used on the system, run the following command and verify the output shows that /dev/shm is mounted. Particular requirements pertaining to mount options are covered in ensuing sections.

# findmnt -kn /dev/shm

Example output:

/dev/shm   tmpfs  tmpfs  rw,nosuid,nodev,noexec,relatime,seclabel

Expected Result

/dev/shm should be mounted as a separate partition with appropriate mount options.

Remediation

Command Line

For specific configuration requirements of the /dev/shm mount for your environment, modify /etc/fstab. Example:

tmpfs   /dev/shm tmpfs   defaults,rw,nosuid,nodev,noexec,relatime,size=2G   0 0

Default Value

Not configured by default.

References

1. https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems/