NGINX - To allow a specific User-Agent from one IP address only

Step 1: Define the Map BlocksAdd this configuration inside the http {} block of your /etc/nginx/nginx.conf file. This logic evaluates the incoming User-Agent and IP address to flag unauthorized requests


http {
    # ... your existing http config ...

    # 1. Check if the User-Agent matches the restricted one
    map $http_user_agent $is_restricted_ua {
        default         0;
        "~*YourCustomUserAgent" 1; # Replace with your target User-Agent (regex matching)
    }

    # 2. Check if the client IP is NOT the authorized one
    map $remote_addr $is_unauthorized_ip {
        default        1;
        "192.168.1.50" 0; # Replace with your ONLY allowed IP address
    }

    # 3. Combine both conditions: Flag if it's the target UA AND an unauthorized IP
    map "$is_restricted_ua$is_unauthorized_ip" $block_request {
        default   0;
        "11"      1; # 1 (Restricted UA) + 1 (Unauthorized IP) = Block
    }
}



Step 2: Apply the Block RuleOpen your website's specific server configuration file (e.g., inside /etc/nginx/sites-available/) and use the combined variable to reject requests with a 403 Forbidden error.

server {
    listen 80;
    server_name yourdomain.com;

    # Place this rule globally inside the server block or inside a specific location block
    if ($block_request) {
        return 403;
    }

    location / {
        # ... your standard site configuration ...
    }
}

Blocking access by user agent in Nginx

 

How to block access by user agent in Nginx. In this configuration, i will use ngx_http_map_module.

Inside http section:

include /etc/nginx/blacklist;

Inside server section (virtual host). We will return 444 status code.

if ($block_ua) {
        return 444;
}

The blacklist file (example)

map $http_user_agent $block_ua {
        default           0;
        ~*profound        1;
        ~*scrapyproject   1;
        ~*netcrawler      1;
        ~*nmap            1;
	~*sqlmap	  1;
	~*slowhttptest	  1;
	~*nikto		  1;
	~*jersey	  1;
	~*brandwatch	  1;
	~*magpie-crawler  1;
	~*mechanize	  1;
	~*python-requests 1;
	~*redback	  1;
}

For testing:

aelius@macbook:~$ curl --head -A "profound" https://www.unixteacher.org/
curl: (52) Empty reply from server

What is http status 444 ?

A non-standard status code used to instruct nginx to close the connection without sending a response to the client, most commonly used to deny malicious or malformed requests.