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Philip Tellis is a geek, speedfreak and Chief RUM Distiller at SOASTA where he works on the mPulse product. mPulse helps site owners measure the real user perceived performance of their sites and help visualize correlations between performance and business metrics like conversions, sales, lolcats and more. You can use mPulse for free at http://www.soasta.com/free.
Every device attached to the Internet is identified by a numeric address known as an IP address. The two forms of IP addresses seen on the open Internet are IPv4, which is a 32-bit number often represented as a series of four decimal numbers separated by dots, e.g. 188.8.131.52, and IPv6 which is a 128-bit number represented as a series of multiple hexadecimal numbers separated by colons, e.g. 2607:f298:1:103::c8c:a407.
In my last article, I spoke about several common mistakes that show up in web applications. Of these, the one that causes the most trouble is insufficient input validation/sanitization. In this article, I'm joined by my colleague Peter (evilops) Ellehauge in looking at input filtering in more depth while picking on a few real examples that we've seen around the web. As you'll see from the examples below, insufficient input validation can result in various kinds of code injection including XSS, and in some cases can be used to phish user credentials or spread malware.
To start with, we'll take an example from one of the most discussed websites today. This example is from a site that hosts WikiLeaks material. Note that the back end code presented is not the actual code, but what we think it might be based on how the exploit works. The HTML was taken from their website. We think it's fair to assume that it's written in PHP as the form's action is index.php.
Web application developers today need to be skilled in a multitude of disciplines. It's necessary to build an application that is user friendly, highly performant, accessible and secure, all while executing partially in an untrusted environment that you, the developer, have no control over. I speak, of course, about the User Agent. Most commonly seen in the form of a web browser, but in reality, one never really knows what's on the other end of the HTTP connection.
There are many things to worry about when it comes to security on the Web. Is your site protected against denial of service attacks? Is your user data safe? Can your users be tricked into doing things they would not normally do? Is it possible for an attacker to pollute your database with fake data? Is it possible for an attacker to gain unauthorized access to restricted parts of your site? Unfortunately, unless we're careful with the code we write, the answer to these questions can often be one we'd rather not hear.