Nginx FastCGI

Unlike other web servers, nginx(8) does not offer a built-in FastCGI implementation.

PHP-FPM

First install and configure PHP-FPM.

nginx(8) just needs to be configured to proxy requests.

location ~ \.php(/|$) {
    fastcgi_split_path_info ^(.+?\.php)(/.*)$;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_param PATH_INFO       $fastcgi_path_info;
    try_files $uri =404;

    fastcgi_pass localhost:9000;
    include fastcgi_params;
}

To use a Unix socket to pass requests, try fastcgi_pass unix:/run/php-fpm/php-fpm.sock;.

Fastcgi_params

Here is a generic fastcgi_params file, which would work for the above example.

fastcgi_param  QUERY_STRING       $query_string;
fastcgi_param  REQUEST_METHOD     $request_method;
fastcgi_param  CONTENT_TYPE       $content_type;
fastcgi_param  CONTENT_LENGTH     $content_length;

fastcgi_param  SCRIPT_NAME        $fastcgi_script_name;
fastcgi_param  REQUEST_URI        $request_uri;
fastcgi_param  DOCUMENT_URI       $document_uri;
fastcgi_param  DOCUMENT_ROOT      $document_root;
fastcgi_param  SERVER_PROTOCOL    $server_protocol;
fastcgi_param  REQUEST_SCHEME     $scheme;
fastcgi_param  HTTPS              $https if_not_empty;

fastcgi_param  GATEWAY_INTERFACE  CGI/1.1;
fastcgi_param  SERVER_SOFTWARE    nginx/$nginx_version;

fastcgi_param  REMOTE_ADDR        $remote_addr;
fastcgi_param  REMOTE_PORT        $remote_port;
fastcgi_param  SERVER_ADDR        $server_addr;
fastcgi_param  SERVER_PORT        $server_port;
fastcgi_param  SERVER_NAME        $server_name;

# PHP only, required if PHP was built with --enable-force-cgi-redirect
fastcgi_param  REDIRECT_STATUS    200;

That final line has to do with crafted URLs. It is desirable in this context.

Hardening

HTTPoxy

To mitigate the HTTPoxy vulnerability, adjust the fastcgi_params file.

fastcgi_param  HTTP_PROXY         "";

Isolation

A common tactic for hardening a FastCGI program is to run php-fpm(8) in a different working directory.

This can lead to issues with the try_files directive, which checks for the existence of a file before responding to a request. On success it overwrites the $uri variable with the local URI. This is a mitigation for embedded PHP attacks.

A workaround is to create empty files in the web root to satisfy try_files.

location ~ \.php(/|$) {
    fastcgi_split_path_info ^(.+?\.php)(/.*)$;
    fastcgi_param SCRIPT_FILENAME /path/to/php/working/directory/$fastcgi_script_name;
    fastcgi_param PATH_INFO       $fastcgi_path_info;
    try_files $uri =404;

    fastcgi_pass localhost:9000;
    include fastcgi_params;
}

Alternatively, replace try_files with a custom instruction.

location ~ \.php(/|$) {
    fastcgi_split_path_info ^(.+?\.php)(/.*)$;
    if (!-f $document_root$fastcgi_script_name) {
      return 404;
    }
}

Fcgiwrap

fcgiwrap(8) is a simple wrapper script that simplifies the configuration and administration of a FastCGI server. See here for help in configuring that server.

nginx(8) just needs to be configured to proxy requests.

location ~ \.php(/|$) {
    fastcgi_param DOCUMENT_ROOT /var/www/cgi-bin/;
    fastcgi_param SCRIPT_NAME   myapp.php;

    fastcgi_pass unix:/run/fcgiwrap.sock;
    include fcgiwrap_params;
}

See here for some details on the configuration.

Spawn-fcgi

spawn-fcgi(1) is a wrapper around the fcgiwrap(8) wrapper script. It comes from the Lighttpd project.

No configuration is necessary, just run the script like:

spawn-fcgi -n -u www-data -p 9000 -- /usr/bin/fcgiwrap -f

Or create a service file to automate this.

Use the same nginx(8) configuration as above.

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