If at first you don't succeed; call it version 1.0
Monday, 18 May 2009

Mikeyy wrote a twitter worm. It’s old news, I know, and by now Twitter seem to fix all the known vulnerabilities on their website.
But, let’s say that there are no more XSS/CSRF/etc. vulnerabilities on Twitter.com. Does it mean that there will be no more twitter worms? Unfortunately, the answer to that question is no.
Even if the guys at Twitter will hire the best security engineer, which will fix all the vulnerabilities on twitter.com, they still have one big issue: Twitter API.
And no, I’m not talking about vulnerabilities in Twitter API, but rather abusing Twitter API as a weak link that can allow the creation of twitter worms.

According to the Twitter Fan Wiki, there are dozens of Twitter services and applications which utilize the Twitter API. It takes only one vulnerability in one of those applications to trigger the next Twitter worm.
An example for this threat is a vulnerability I found a few weeks ago in twitpic.com website.
twitpic.com imports the profile information from twitter, and displays it on the twitpic.com profile page. While twitter.com (finally) sanitize and encode HTML tags in the twitter profile information (name, URL, bio, etc.), twitpic.com failed to do so and by that allowed injecting scripts to the twitpic user profile page. This is a very simple persistent XSS, which can be easily abused to hijack twitpic.com user accounts. However, because twitpic.com also uses the Twitter API to automatically send twits on behalf of the user, whenever the user uploads a picture or comments on another user’s picture, it can also be easily used to create a Twitter worm.
I’ve created a proof of concept, which automatically comments on a random picture on twitpic.com, whenever a user visits the twitpic.com profile of the user I created – “twitpicxss”. This could have caused anyone who visits the profile page, and was logged in to twitpic.com, to automatically send a twit on twitter.com with the content I set in the comment. The content contained a link to the “twitpicxss” profile, which could have made other users, who follow the victim, to click on that link, be exploited, and keep spreading the worm.
I’ve reported this vulnerability to twitpic.com, and they have fixed it on the same day. But again, this is just one example. As I said, there are many services and applications out there that use the Twitter API. Some of them are probably vulnerable too.


Twitter are not alone in this mess. This “Cross-Web2.0 Scripting” type of vulnerabilities can affect all other social networks with open API (e.g. Facebook, LinkedIn).
In conclusion, if you are the owner of a service which provides an API, fixing your own website or application vulnerabilities might not be enough…


Monday, 18 May 2009 22:40:14 UTC | Comments [2] | Security#
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The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway.