I wrote a Perl module that can be used to block HTTP requests from open proxies. The intended purpose is to prevent bogus form submissions.

Before the request is further processed, the module grabs REMOTE_ADDR and does the following:

• Takes a few ports that are commonly used by open proxies and lets Nmap [nmap.org] determine which of those ports are open at REMOTE_ADDR.
  
• Attempts to use each of the open ports as a proxy, and if any of the requests would succeed, sends a 403 error and exits.
  

Once the module has been configured and installed, and assuming that Perl is the programming language, all I need to do is inserting these two lines in the beginning of the form processing script:

use HTTP::ProxyTest; 
proxytest(); 

I would appreciate your comments on this approach to deal with bogus form submissions from open proxies.

[edited by: phranque at 5:25 am (utc) on May 11, 2009]
[edit reason] personal url. See TOS [webmasterworld.com] [/edit]