How was the vulnerability discovered?
I found the vulnerability by manually investigating and reverse engineering the binary code of QuickTime and created a fuzzer to cover specific portions of the Apple media formats. In this particular vulnerability, QuickTime does not parse .pct media files properly, which causes a corruption in the module DllMain through a malformed file with an invalid value located at offset 0x20E. In my testing I used QuickTime Player version 7.7.1 (1680.42) on Windows XP SP 3 - PT_BR, but most likely other versions on Windows affected as well.
A PoC repro01.pct is available for interested parties and was shared with Apple on February 22, 2012 to help them locate and fix the problem.
What does this vulnerability mean?
If you use QuickTime, attackers can take total control of your machine through this vulnerability, which is triggered by playing a malicious media file that uses overly large values in the PCT image format. A typical attack would embed such a file into a webpage and use social engineering to drive users into viewing the page. So far, there have been no reports of attackers exploiting this vulnerability yet.
To put this into context, QuickTime is used by 61% of all internet enabled PCs, including 49% of all Windows PCs and 98% of all Apple computers (numbers courtesy of Qualys BrowserCheck). Even if you don't use QuickTime by default to play movies and videos, it can be used as the media player for the PCT format on all web browsers, including Chrome, Safari, Internet Explorer and Firefox.
All users, consumers and businesses alike, should download the security update as soon as possible since simply browsing to a malicious web page on any web browser can activate this vulnerability. If you're not sure whether your QuickTime plug-in is updated, you can use Qualys BrowserCheck, a free service, to check if you need to download the update.
Throughout the whole process, Apple was very professional in handling this issue and provided constant status updates upon my request. It was great to see a company of Apple's size taking a proactive role to ensure that their software and their users are protected from major vulnerabilities like this one.
Author: Rodrigo Branco, Director of Vulnerability and Malware Research at Qualys.