Is someone trying to hack my site? How to block certain URLs in Nginx?

Question

On the past few hours my server is getting pretty loaded, mostly due to a lot of load requests. I've seen this thanks to the StatCounter realtime stats, which shows that the "Came from" page is:

http://www.facebook.com/extern/login_status.php?api_key=3d34061e0ac6dc4dec21b35d2fb9d6d3&extern=0&channel=http%3A%2F%2Fwww.mysite.com%2F%3Fxd_receiver%3D1&locale=es_ES&sdk=edgar

And the Landing Page is

http://www.mysite.com/?xd_receiver=1#%7B%22id%22%3A0%2C%22sc%22%3A%22http%3A%2F%2Fwww.facebook.com%2Fxd_receiver_v0.4.php%22%2C%22sf%22%3A%22loginStatus%22%2C%22sr%22%3A2%2C%22h%22%3A%22loginServer%22%2C%22sid%22%3A%220.162%22%2C%22t%22%3A0%7D%5B0%2C%22loginStatus%22%2C%22InitLogin%22%2C%7B%22b

The CPU, mem and bandwidth are getting higher and higher, and I'd like to now if this could be some sort of attack.

This is a WordPress blog with WP 3.2.1, based on an Ubuntu 10.04.2 LTS, with Nginx, PHP-FPM and APC. Usually it runs pretty well, but I'm affraid this requests are loading the server to much.

The only explanation I have is that I've got the Simple Facebook Connect plugin to allow comments with a Facebook account, but it hasn't give any problems until now.

The strange thing is, the access.log shows the requests come from different IPs, so I guess it's not an attack

164.77.106.237 - - [19/Oct/2011:18:20:53 +0200] "GET /?xd_receiver=1 HTTP/1.1" 403 189 "http://www.facebook.com/extern/login_status.php?api_key=3d34061e0ac6dc4dec21b35d2fb9d6d3&extern=0&channel=http%3A%2F%2Fwww.mysite.com%2F%3Fxd_receiver%3D1&locale=es_ES&sdk=edgar" "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; InfoPath.1)"
212.104.164.139 - - [19/Oct/2011:18:20:48 +0200] "GET /?xd_receiver=1 HTTP/1.1" 403 135 "http://www.facebook.com/extern/login_status.php?api_key=3d34061e0ac6dc4dec21b35d2fb9d6d3&extern=0&channel=http%3A%2F%2Fwww.mysite.com%2F%3Fxd_receiver%3D1&locale=es_ES&sdk=edgar" "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/14.0.835.202 Safari/535.1"

etc.

Is it possible in Nginx to block URLs for example that match the api_key parameter that is a constant in all these requests?

Answer 1

Yes, you can block an url in NGINX with regex like this:

location / {
    if ($uri ~* '^/(abc|def|ghi)$') {
         allow 1.2.3.4;
         deny all;
    }
    root  /var/www/
    ...
}

You can also block some referers:

if ($http_referer ~* (klm|nop|qrs)) {
    return 403;
}

Or user agent:

if ($http_user_agent ~ (libwww-perl|wget) ) {
    return 403;
}