Month of Apple Bugs - Day 6 Fix Released

07 Jan 2007, 21:41 PST

Today's Patch

After much wrangling, I've cooked up a patch for the denial of service bug in Apple's PDF implementation, detailed in MOAB-06-01-2007.

The patch implements loop detection in CoreGraphic's CGPDFReaderGetPageDictionary(), safely exiting the loop after 500,000 iterations (takes approximately 1 second on my machine). By way of comparison, the full ISO C99 specification PDF hits a maximum recursion count of 24. I'd like to thank the venerable William Carrel for his time reviewing the code, and his ideas on implementing recursive functional call handling. Thanks also to Rosyna of Unsanity for assisting in debugging Core Graphics.

The patch prevents the proof-of-concept PDF from locking up any application that uses the CoreGraphics PDF library, including Safari and Since we're unable to patch mdimporter, it will still temporarily fall into an infinite loop on nefarious PDF files -- fortunately, mdimporter detects the loop and exits.

You can download the source, or the pre-built binary. This release removes the VLC fix, so make sure that your VLC player is up to date.

MoAB Collaboration

I'd like to thank everyone for your input.

As I previously stated, I respectfully disagree with the decision to release exploits with no vendor notification. I must also stress that I am not a security researcher, and as such I strongly prefer to recuse myself from the heated debate and focus on providing fixes.

I think that I will have to respectfully decline LMH's offer of coordination. I genuinely appreciate the gesture of goodwill, but I don't feel that it is the right thing to do. I know some of you will disagree with me (and some will agree) -- but upon further reflection, I can't personally compromise the ethical point, though the offer may make my life easier.

I hope you'll all understand, and we can get back to bug fixes quickly. A sincere "thanks" to LMH and MoAB for the offer.