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Mitigate SQL Injection Attacks on Legacy ASP Sites

For those of you, like me, that have to support old sites for your clients, dealing with the vulnerabilities of old code can be quite a hassle.  Especially now that the best documented and known exploits can be completely automated.  One of our clients was recently subject to such an attack.  Unfortunately, when the site was originally developed, no real security was built into the code.  One user posted all SQL requests, no matter if it was coming from the public side or the admin side. All requests came directly from the page, meaning that every page had the code, and every one would have to be touched to really fix it.

As we were already redeveloping the modern replacement to the site, the client wanted us to spend as little time as possible on the old one.  So a true security audit was out of the question.  This, of course, is still the right way to solve the problem, but right isn't always in the budget.  So that leads us to a couple tools to help avoid the problem until we could release the replacement site.

The first is a tool from Microsoft called URLScan. URLScan has a lot of features, but what we used it for here was to limit the length of query strings.  Since the attack strings were almost always longer than a regular POST or GET, we just had to limit the length of the strings for most of those attacks to fail. Take a look at it, there's lots of neat tricks URLScan can do.

The big gun we used was an ISAPI filter written by Rodney Viana.  It's designed to scrub GET and POST requests of anything that would look like an attack.  It has been a life saver, especially when the attacks were happening hourly.


Posted by Wayne Walton on Monday, June 16, 2008 10:50 AM
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