cis-ubuntu2004-v300-7-1-9

DevOps & Security

Ensure access to /etc/shells is configured

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_20.04_LTS_Benchmark_v3.0.0/cis-ubuntu2004-v300-7-1-9/SKILL.md

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7.1.9 Ensure access to /etc/shells is configured (Automated)

Profile

Level 1 - Server
Level 1 - Workstation

Description

/etc/shells is a text file which contains the full pathnames of valid login shells. This file is consulted by chsh and available to be queried by other programs.

Rationale

It is critical to ensure that the /etc/shells file is protected from unauthorized access. Although it is protected by default, the file permissions could be changed either inadvertently or through malicious actions.

Impact

None

Audit Procedure

Command Line

Run the following command to verify /etc/shells is mode 644 or more restrictive, Uid is 0/root and Gid is 0/root:

# stat -Lc 'Access: (%#a/%A) Uid: ( %u/ %U) Gid: ( %g/ %G)' /etc/shells

Expected Result

Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)

Remediation

Command Line

Run the following commands to remove excess permissions, set owner, and set group on /etc/shells:

# chmod u-x,go-wx /etc/shells
# chown root:root /etc/shells

Default Value

Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)

References

NIST SP 800-53 Rev. 5: AC-3, MP-2

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	3.3 Configure Data Access Control Lists	X	X	X
v7	14.6 Protect Information through Access Control Lists	X	X	X

MITRE ATT&CK Mappings:

Techniques / Sub-techniques	Tactics	Mitigations
T1003, T1003.008, T1222, T1222.002	TA0005	M1022