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cis-ubuntu1804-v220-1-1-8-3

DevOps & Security
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Ensure nosuid option set on /dev/shm partition

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_18.04_LTS_Benchmark_v2.2.0/cis-ubuntu1804-v220-1-1-8-3/SKILL.md

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Ensure nosuid option set on /dev/shm partition

Profile

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

Description

The nosuid mount option specifies that the filesystem cannot contain setuid files.

Rationale

Setting this option on a world-writable directory, to prevent users from creating setuid files in shared memory, reduces the risk of privilege escalation through setuid exploitation.

Impact

None noted.

Audit Procedure

Command Line

Verify that the nosuid option is set for the /dev/shm mount.

# findmnt -kn /dev/shm | grep nosuid

Expected Result

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

Remediation

Command Line

Edit the /etc/fstab file and add nosuid to the fourth field (mounting options) for the /dev/shm partition. It is recommended that /dev/shm is mounted as tmpfs.

# Example:
tmpfs   /dev/shm   tmpfs   defaults,rw,nosuid,nodev,noexec,relatime   0 0

# Run the following command to remount /dev/shm with the configured options:
mount -o remount /dev/shm

Note: Some distributions may mount /dev/shm through other means (e.g. systemd). If this is the case, verify that the mount options are configured correctly in the relevant configuration file.

Default Value

Not set by default on all distributions.

References

  1. See the fstab(5) manual page for more information.
  2. NIST SP 800-53 Rev. 5: AC-3, MP-2

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: T1548, T1548.001 (TA0005) - M1038