Web Application Defender's Cookbook

Recipe 4-2: Identifying Suspicious Open Proxy Usage

This recipe demonstrates how to use the MaxMind GeoIP database data to identify when clients are using open proxy servers from geographic regions that are different from where they live.

Ingredients

• MaxMind’s GeoLite City Database2
• ModSecurity
  • SecGeoLookupDb directive
  • @geoLookup action
  • GEO variables

The use of open proxy servers by itself does not equate to malicious intent. A client might not want to connect to a web site directly for a variety of legitimate privacy reasons. Furthermore, many proxying scenarios related to various ISPs for mobile clients dynamically reroute clients through caching proxy servers and then onto the destination site if content is unavailable. These scenarios mainly utilize proxy servers within the same geographic country codes. Malicious clients, on the other hand, routinely route their traffic through proxy servers from different countries. Their motivation for doing so is to make IP traceback efforts more challenging. Let’s look at these requests. Here is a sample ModSecurity audit log entry for a proxy request:

--f2e56119-A--
[05/Jan/2012:11:47:13 --0600] hbhwWsCo8AoAABc8eGUAAAAb 220.255.1.40 57253 192.168.240.10 80 --f2e56119-B-- GET /demo.testfire.net/ HTTP/1.1 Host: www.modsecurity.org Connection: keep-alive User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.63 Safari/535.7 Accept: */* Accept-Encoding: gzip,deflate,sdch Accept-Language: ...