Cis Ubuntu2004 V300 1 1 2 4 1

---
name: cis-ubuntu2004-v300-1-1-2-4-1
description: "Ensure separate partition exists for /var"
category: cis-storage
version: "3.0.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-20.04, partition]
cis_id: "1.1.2.4.1"
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

## Profile

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

## Description

The `/var` directory is used by daemons and other system services to temporarily store dynamic data. Some directories created by these processes may be world-writable.

## Rationale

The reasoning for mounting `/var` on a separate partition is as follows.

The default installation only creates a single `/` partition. Since the `/var` directory may contain world writable files and directories, there is a risk of resource exhaustion. It will essentially have the whole disk available to fill up and impact the system. In addition, other operations on the system could fill up the disk unrelated to `/var` and cause unintended behavior across the system as the disk is full. See `man auditd.conf` for details.

Configuring `/var` 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. Other options allow for specific behavior. See `man mount` for exact details regarding filesystem-independent and filesystem-specific options.

An example of exploiting `/var` may be an attacker establishing a hard-link to a system `setuid` program and waiting for it to be updated. Once the program was updated, the hard-link can be broken and the attacker would have their own copy of the program. If the program happened to have a security vulnerability, the attacker could continue to exploit the known flaw.

## 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` is mounted.
Example:

```bash
# findmnt -kn /var
```

Example output:

```
/var   /dev/sdb  ext4   rw,nosuid,nodev,relatime,seclabel
```

## Expected Result

`/var` 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`.
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` 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/
2. NIST SP 800-53 Rev. 5: CM-7
3. RHEL 8 STIG Vul ID: V-244529
4. RHEL 8 STIG Rule ID: SV-244529r902737

## CIS Controls

v8 - 3.3 Configure Data Access Control Lists (IG 1, IG 2, IG 3)
v7 - 14.6 Protect Information through Access Control Lists (IG 1, IG 2, IG 3)

MITRE ATT&CK Mappings: T1499, T1499.001 | TA0006 | M1022