Facebook Users Targeted by Cross-Site Scripting Exploit

Wednesday, March 30, 2011

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Facebook's security team is working to mitigate problems caused by a cross-site scripting (XSS) flaw that was exploited by attackers to infect user accounts with a self-propagating worm.

The attack affected users whether or not they had enabled the SSL option (https) recently offered by the social network to improve security.

The vulnerability was caused by inadequate JavaScript validation, which allowed attackers to post messages on the profile wall of any logged-in Facebook user who happened across an infected webpage.

Facebook users were lured to the infected websites with specially designed spam, and the messages posted to their profile profile walls contained links to infected sites, which caused the worm to spread rapidly across the network.

From Symantec's Candid Wueest:

"The vulnerability exists in the mobile API version of Facebook due to insufficient JavaScript filtering. It allows any website to include, for example, a maliciously prepared iframe element that contains JavaScript or use the http-equiv attribute’s “refresh” value to redirect the browser to the prepared URL containing the JavaScript."

"Any user who is logged into Facebook and visits a site that contains such an element will automatically post an arbitrary message to his or her wall. There is no other user interaction required, and there are no tricks involved, like clickjacking."

"Just visiting an infected website is enough to post a message that the attacker has chosen. Therefore it should be of no surprise that some of those messages are spreading very fast through Facebook. Some are posting links to infected websites, creating XSS worms that spread from user to user."

Facebook has patched the JavaScript-based XSS vulnerability, and the company says they are now working to undo the damage done by the attack.

Source: http://www.symantec.com/connect/blogs/new-xss-facebook-worm-allows-automatic-wall-posts

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