cis-nginx-v300-2-5-1

DevOps & Security

Ensure server_tokens directive is set to off (Manual)

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CIS 2.5.1 — Ensure server_tokens directive is set to `off`

Profile Applicability

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

Description

The server_tokens directive is responsible for displaying the NGINX version number and operating system version on error pages and in the Server HTTP response header field. This information should not be displayed.

Rationale

Attackers can conduct reconnaissance on a website using these response headers, then target attacks for specific known vulnerabilities associated with the underlying technologies. Hiding the version will slow down and deter some potential attackers.

Impact

None. Disabling server tokens does not affect functionality. It merely removes the version string from error pages and headers. Note that determined attackers can still fingerprint NGINX via other methods, but removing the banner raises the bar for opportunistic scanners.

Audit Procedure

In the NGINX configuration file nginx.conf, verify the server_tokens directive is set to off. To do this, check the response headers for the server header by issuing this command:

curl -I 127.0.0.1 | grep -i server

The output should not contain the server header providing your server version, such as the below:

Server: nginx/1.28.0

Remediation

Disable version disclosure globally by adding the directive to the http block in /etc/nginx/nginx.conf:

http {
    ...
    server_tokens       off;
    ...
}

Default Value

The default value of server_tokens is on.

References

https://nginx.org/en/docs/http/ngx_http_core_module.html#server_tokens

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	16.1 Establish and Maintain a Secure Application Development Process	N	Y	Y
v7	18.1 Establish Secure Coding Practices	N	Y	Y

MITRE ATT&CK Mappings

Tactic	Technique
Reconnaissance	T1592 - Gather Victim Host Information

Profile

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