Nginx - Content injection

/etc/nginx/sites-enabled/example.com.conf

server {
    listen 80;
    server_name example.com www.example.com;
    
    root /var/www/example.com;
    index index.html;
    
    # Using Nginx's ngx_http_sub_module module to modify the request content
    # Ref. http://nginx.org/en/docs/http/ngx_http_sub_module.html
    
    # Inject an HTML element
    sub_filter '<body>' '<body><br/><h1>Hello! this is an injected content 💉</h1>';
    
    # Inject a script that will show an alert on window click
    sub_filter '</head>' '<script language="javascript">window.onclick=function(){alert("Hello from injected script!")}</script></head>';
    
    sub_filter_once on;
}

Definition

sub_filter will replace the text with another text.
sub_filter_once on; set to on to only replace the first occurence.

lnxph-devops-sareno/nginx-content-injection.md

Nginx - Content injection

Definition