(Collaborative post by Mateusz “j00ru” Jurczyk and Gynvael Coldwind)
Almost five months ago, Gynvael Coldwind and I wrote about an effort to improve the security of popular PDF parsing and rendering software; back then, we were primarily focused on the Chrome PDF Renderer and latest Adobe Reader applications. In order to achieve our results, we used several hundred CPU cores to create a unique, minimal set of PDF documents aimed at optimal code coverage. That corpus, which we now consider a fundamental part of our bug hunting success, was used as fuzzing input to numerous mutation algorithms (basic bitflipping, undisclosed PDF-specific algorithms that respect the primary rules of a document’s structure, and things in between).
As a quick recap, we found more than 50 vulnerabilities ranging from low (unlikely exploitable) to high (serious memory errors) severity in the PDF-parsing component of Google Chrome with the help of AddressSanitizer. All of these were fixed by the Chrome Security Team by August 2012, mostly by Chris Evans – kudos! In addition to that, we also reported around 60 Adobe Reader crashes appearing to be unique in June last year. This consequently resulted in a total of 25 separate fixes addressed by 12 CVEs, as described by the Adobe in their APSB12-16 security bulletin and implemented in the new 9.5.2 and 10.1.4 versions of the software for Windows and Mac OS X platforms. Unfortunately, a few very important questions remained unanswered, such as “what about the remainder of the reported bugs?” and “what about the security of Reader for Linux users?”. With Adobe releasing new versions for all supported Reader branches and platforms today (9, X, XI for Windows, Mac OS X and Linux), we would like to take the chance to give you an update on where we stand with PDF fuzzing, and what thoughts we have around Reader and the many other pieces of software people use in their daily work with documents.
Let’s start with Google Chrome – has anything changed since our last posting? Well, we’ve kept playing with different fuzzing configurations and algorithmic approaches, and discovered 20 new security issues over the last six months, summing up to a total of 78 unique bugs found and fixed in the renderer in 2012. As of now, we are not aware of any unfixed non-DoS issues in the PDF Chrome component.
                Medium CVE-2012-2875: Various lower severity issues in the PDF viewer. Credit to Mateusz Jurczyk of Google Security Team, with contributions by Gynvael Coldwind of Google Security Team.