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July 27, 2011

Advisory: NAB Credit Card Envelope Information Disclosure Vulnerability

I recently ordered some new credit cards, two sets of two (makin’ it rain baby), and they arrived in the post today in two separate envelopes. National Australia Bank (NAB) send out their cards in unmarked white envelopes, which is good, what’s not so good is that the embossed number on the card gets permanently imprinted into the plastic window of the envelope – presumably due to the pressure of having other envelopes on top of it. As a result, with the right lighting, I was able to read the full card number before I even opened the envelope (blurry snapshot below). It’s probably worth noting that the number will still be legible after the recipient has disposed of the envelope in the trash.

One can argue that having just the card number on its own is not as useful. But remember you’re holding an addressed envelope, so you have the cardholder’s name and address, including post code. You also know the start date on the card, which will almost always be the current month (sometimes the following month), and due to the fact that most credit cards have a lifespan of three years, you can also deduce the year of expiry. The month of expiry may or may not be the same as the start month. The only thing missing is the CVV, but then again there are still plenty of places that don’t require those. With just the card number, an attacker could clone it onto a fake credit card, and start using it in shops with any random signature.

Although this post is intended to be tongue-in-cheek, it probably wouldn’t hurt for NAB (or their card printing company) to fix this ‘vulnerability’. What would PCI say? :D

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