cis-nginx-v300-4-1-3

name	cis-nginx-v300-4-1-3
description	Ensure private key permissions are restricted (Manual)
category	cis-nginx
version	3.0
author	cyberstrike-official
tags	["cis","nginx","web-server","reverse-proxy","tls-ssl","encryption"]
cis_id	4.1.3
cis_benchmark	CIS NGINX Benchmark v3.0.0
tech_stack	["nginx","linux","web-server"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS 4.1.3 — Ensure private key permissions are restricted

Profile Applicability

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

Description

The server's and potentially its vhost's private keys should be protected from unauthorized access by limiting access based on the principle of least privilege.

Rationale

A server's private key file should be restricted to 400 permissions. This ensures only the owner of the private key file can access it. This is the minimum necessary permissions for the server to operate. If the private key file is not protected, an unauthorized user with access to the server may be able to find the private key file and use it to decrypt traffic sent to your server.

Audit Procedure

Verify the permissions on the key file are 400. This can be found by running the following command. You should replace /etc/nginx/nginx.key with the location of your key file.

find /etc/nginx/ -name '*.key' -exec stat -Lc "%n %a" {} +

The output should show mode 400 or more restrictive.

Example:

/etc/nginx/nginx.key 400

Remediation

Run the following command to remove excessive permissions on key files in the /etc/nginx/ directory.

Note: The directory /etc/nginx/ should be replaced with the location of your key file.

find /etc/nginx/ -name '*.key' -exec chmod u-wx,go-rwx {} +

Default Value

The default permissions on the server's private key are 644 or -rw-r--r--.

References

1. https://nginx.org/en/docs/http/configuring_https_servers.html

Additional Information

Important Note: This recommendation should be applied to both the keys of your server certificate and the key of your client certificate if you are looking to mutually authenticate a proxy server.

CIS Controls