Wordpress Nginx Won't 404

Question

I have nginx running wordpress. Weird thing is the site won't 404 and instead rewrites the URL to the homepage. Any URL with a .php in the string will 404 correctly but /foo will not 404. Any help would be appreciated.

example.com/foo.php will 404

example.com/foo will not 404 and instead just loads the homepage.

    location / {
            # This is cool because no php is touched for static content.
            # include the "?$args" part so non-default permalinks doesn't break when using query string
            try_files $uri $uri/ /index.php?$args;
    #try_files $uri $uri/ =404;
    }
# pass the PHP scripts 
#
location ~ \.php$ {
            fastcgi_intercept_errors on;
    include snippets/fastcgi-php.conf;
    # With php7.0-fpm:
    fastcgi_pass unix:/run/php/php7.0-fpm.sock;
}

error_page 404 = /404.html;
location = /404.html {
    root /home/web/error-pages;
    internal;
}

I've been able to narrow this down to my nginx (Ubuntu 16.04, PHP 7, MySQL) because even a fresh install of WordPress has the same behavior.

Answer 1

I did a test on a fresh install of WordPress 6.0.1, served using php-fpm 7.4.3 and nginx 1.18.0 on Ubuntu 20.04.4 using this nginx configuration:

server {
    listen 80;
    server_name wp.test;

    root /var/www/wp;
    index index.php;

    location / {
        try_files $uri $uri/ /index.php?$args;
    }

    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/var/run/php/php-fpm.sock;
    }
}

(I also added to 127.0.0.1 wp.test to /etc/hosts).

Observation: accessing a URL that is supposed to be non-existent (e.g. http://wp.test/nonexistent) would show the contents of the home page (i.e. exactly the same content as http://wp.test/). This is unexpected, strange, and incorrect behavior.

I do not understand the cause of the behavior, but I found that it is possible to "fix" the problem by changing the permalink settings in the WordPress admin area. The problem only seems to affect the "Plain" permalink setting. The problem disappears when using another permalink structure. For example, with the "Post name" permalink setting, accessing http://wp.test/nonexistent would show a 404 error.