Tom's corner of the internet

Purchasing a £30,000 numberplate for the price of a bus ticket

October 07, 2013 - Under: is a website that allows you to purchase customized numberplates for your car or motorbike. They boast a large number of famous clients and short numberplates are often on sale for upwards of £20,000 (the plate ABC 4 is up for £30,000). While playing with their site I discovered a flaw that would allow anybody to purchase that ABC 4 plate for an arbitrary price. As always I waited until the issue was fixed on the site before publishing this post.

The order process

The order process is simple and painless. You search for a numberplate and browse ones available for purchase. Once you have found one that you like you select “Buy” and you are taken to a page where you can enter your personal details:

proper total JKMOZWWG

Within the order page there is a form element with some interesting names:

vuln form 5F5IOWYK

Surely the site would validate the input to ensure no negative values could be added?

modified form YQGDI4LB

Or not

order total A2ROBCPV

And finally the payment page:

purchasing 4QISBW5X

I would have certainly been able to complete the payment but whether or not the order would have succeeded depends on how automated is. I doubt it’s completely automated so I expect someone along the line would have flagged this up and stopped the transfer, but who knows? This goes to show that while using a framework can protect you against common flaws like SQL injection or XSS business logic still needs to be tested and inputs still need to be validated.

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Written by Tom Forbes who lives and works in London building useful things with Python and Django. I usually blog about security, my projects and random experiments