cis-nginx-v300-2-4-3

DevOps & Security

Ensure keepalive_timeout is 10 seconds or less, but not 0 (Manual)

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CIS 2.4.3 — Ensure keepalive_timeout is 10 seconds or less, but not 0

Profile Applicability

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

Description

Persistent connections are leveraged by all modern browsers to facilitate greater web performance. The keep-alive timeout limits the time a persistent connection may remain open. Setting the keep-alive timeout allows this timeout to be controlled on the server side.

Rationale

Setting a keep-alive timeout on the server side helps mitigate denial of service attacks that establish too many persistent connections, exhausting server resources.

Impact

Setting the keepalive_timeout to a low value may impact performance for clients with high-latency connections or applications that require long-lived connections.

Audit Procedure

To check the current setting for the keepalive_timeout directive, issue the below command. You should also manually check your nginx configuration for include statements that may be located outside the /etc/nginx directory. If none of these are present, the value is set at the default.

grep -ir keepalive_timeout /etc/nginx

The output of the command should contain something similar to the following:

keepalive_timeout 10;

Remediation

Find the HTTP or server block of your nginx configuration, and add the keepalive_timeout directive. Set it to 10 seconds or less, but not 0. This example command sets it to 10 seconds:

keepalive_timeout 10;

Default Value

By default, this timeout is dictated by the user agent and varies. It is not set on the server side by default.

References

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

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
Impact	T1499 - Endpoint Denial of Service

Profile

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