EC
444
HTTPERRORNotable4xx Client Error (Unofficial)HIGH confidence

No Response

Production Risk

Low — when used correctly this is a useful security measure. Incorrectly applied, it can silently block legitimate clients.

What this means

444 No Response is an nginx-specific status code used internally to instruct nginx to close the connection immediately without sending any response to the client. It is typically used to block malicious or unwanted requests silently.

Why it happens
  1. 1nginx is configured to silently drop certain requests (e.g., from known bad bots or attackers) using return 444.
  2. 2A security rule or rate-limiting rule in nginx matched the request and is blocking it with no response.
  3. 3Legitimate clients will never see this code — it causes the connection to be dropped, appearing as a connection refused or reset to the client.
How to reproduce

An automated scanner or bot hits an nginx server configured to block it silently.

trigger — this will error
trigger — this will error
# nginx.conf
server {
    if ($http_user_agent ~* (masscan|nikto|sqlmap)) {
        return 444;
    }
}

expected output

Connection reset by peer (no HTTP response sent)

Fix

Use 444 to silently block malicious bots

WHEN You want to drop attacker connections without revealing server information.

Use 444 to silently block malicious bots
# nginx.conf — block empty User-Agent (common in scanners)
if ($http_user_agent = "") {
    return 444;
}

Why this works

Drops the TCP connection immediately, giving attackers no information about the server.

What not to do

✕ Do not use 444 for legitimate API rejections

Use 400, 401, or 429 so legitimate clients receive a useful error message.

Version notes
nginx

nginx-internal only. The client receives a TCP connection close, not an HTTP response.

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