cis-nginx-v300-2-2-3

DevOps & Security

Ensure the NGINX service account has an invalid shell (Manual)

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CIS 2.2.3 — Ensure the NGINX service account has an invalid shell

Profile Applicability

Level 1 - Webserver
Level 1 - Proxy
Level 1 - Loadbalancer

Description

The NGINX service account must be configured with an invalid login shell to prevent interactive access.

Rationale

The NGINX service account is strictly for running daemon processes. Assigning it a valid login shell (like /bin/bash) unnecessarily expands the attack surface. If an attacker compromises the account credentials (or adds an SSH key), a valid shell facilitates interactive system access. Setting the shell to /sbin/nologin or /bin/false ensures that even with valid credentials, the system immediately rejects a login attempt.

Impact

None. Service accounts do not require interactive login capabilities for normal operation.

Audit Procedure

1. Identify the User:

nginx -T 2>/dev/null | grep -i "^user"

(Note the user, e.g., nginx)

2. Verify Shell:

Run the following command to inspect the configured shell for the identified user:

getent passwd nginx

(Replace nginx with the actual user found in step 1)

Evaluation:

Examine the last field of the output (the shell).

PASS: The shell is set to /sbin/nologin, /bin/nologin, or /bin/false.
FAIL: The shell is set to /bin/bash, /bin/sh, or any other interactive shell listed in /etc/shells.

Example Output (PASS):

nginx:x:999:988:nginx user:/nonexistent:/usr/sbin/nologin

Remediation

Change the login shell for the identified user to /sbin/nologin:

usermod -s /sbin/nologin nginx

(Replace nginx with the actual user)

Default Value

Official packages typically configure the user with /sbin/nologin or /bin/false by default.

References

https://nginx.org/en/docs/ngx_core_module.html#user

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	4.1 Establish and Maintain a Secure Configuration Process	Y	Y	Y
v7	5.1 Establish Secure Configurations	Y	Y	Y

MITRE ATT&CK Mappings

Tactic	Technique
Privilege Escalation	T1078 - Valid Accounts

Profile

Level 1 - Webserver
Level 1 - Proxy
Level 1 - Loadbalancer