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The Danger of Abitrary Strings

April 22nd, 2008

A friend of mine recently pointed out a rather unique “feature” that cnn.com appears to be introducing: the ability to print headlines directly to a t-shirt for, I don’t really know… live blogging purposes? Maybe.

Anyway, whether by his own brilliance or act of God, Tom noted that the webpage used to generate these print-on-demand t-shirts is nothing more than your average GET string. So, when you click on the headline “Nail polish color may tip off politics” the browser sends that string to the t-shirt generator as the URL “headline=Nail%20polish%20color%20may%20tip%20off%20politics”. But, GET strings have significant security implications, in that it is trivial for the end user to alter those strings, resulting in rather humorous results.

For example, you could request a t-shirt that says “CNN is stupid“. Tom had other ideas. I figured, if you can say something silly, what’s to stop you from saying something newsworthy.

Just in case CNN fix this little glitch, here’s a snapshot of the last link’s output

As Tom noted, it seems all very familiar. While CNN was stupid enough to allow their tool to be used for subversive ends, they learned Nike’s lesson and prohibit you from actually purchasing t-shirts with unauthorized headlines. Which gets to the point of this post. Developers of applications are often looking for flexibility in the constant drive to make code do whatever the client requests. My own company is certainly not immune to this siren’s call. But sometimes that flexibility can lead to real issues..

The right way to build such a t-shirt tool is to pass a unique ID to that t-shirt application that corresponds to the particular story in the CNN database. The tool then goes and fetches the headline and publication date and prepares a delightful, non-embarrassing, headline t-shirt. Of course, that leads to the dreaded coupling, where two seemingly unrelated pieces of technology become reliant on one another… a significant violation of the Agile principles. But you know what, I think I prefer heresy over being fired.

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