Two researchers yesterday won $10,000 each at the Pwn2Own hacking contest by bypassing important security measures of Windows 7.
Both Peter Vreugdenhil of the Netherlands and a German researcher who would only identify himself by the first name Nils found ways to disable DEP (data execution prevention) and ASLR (address space layout randomization), which are two of Windows 7’s most vaunted anti-exploit features. Each contestant faced down the fully-patched 64-bit version of Windows 7 and came out a winner.
Vreugdenhil used a two-exploit combination to circumvent first ASLR and then DEP to successfully hack IE8. A half-hour later, Nils bypassed the same defensive mechanisms to exploit Mozilla’s Firefox 3.6. For their efforts, each was awarded the notebook they attacked, $10,000 in cash and a paid trip to the DefCon hackers conference in Las Vegas this July.
“Every exploit today has been top-notch,” said Aaron Portnoy, security research team lead at 3Com’s TippingPoint security unit, the sponsor of the contest, in an interview at the end of the day Wednesday. “The one on IE8 was particularly impressive.”
Vreugdenhil, a freelance vulnerability researcher, explained how he bypassed DEP and ASLR. To outwit ASLR — which randomly shuffles the positions of key memory areas to make it much more difficult for hackers to predict whether their attack code will actually run — Vreugdenhil used a heap overflow vulnerability that allowed him to obtain the base address of a .dll module that IE8 loads into memory. He then used that to run his DEP-skirting exploit.
DEP, which Microsoft introduced in 2004 with Windows XP Service Pack 2, prevents malicious code from executing in sections of memory not intended for code execution and is a defense against, among other things, buffer-overflow attacks.
“[The exploit] reuses Microsoft’s own code to disable DEP,” said Vreugdenhil. “You can reuse Microsoft’s own code to disable memory protection.”
In a paper he published today (download PDF), Vreugdenhil spelled out in more detail how he evaded both ASLR and DEP.
“It was a two-step exploitation,” Vreugdenhil said of the unusual attack. “I could have done it with one, but it would have taken too long.” Using the double-exploit technique gave him control of the machine in a little over two minutes; if he had used only one exploit, the task would have required 50 to 60 minutes.
“I didn’t know how much time I would have at Pwn2Own,” he said, referring to the constraints of the contest, where hackers had limited time slots. And he didn’t want to bore his audience. “I put some eye candy in the exploit,” he said, referring to a progress bar he inserted that read “Please be patient while you are being exploited…”
“It feels great,” said Vreugdenhil of winning. “But I was nervous. I was convinced that there would be other exploits for IE8.” This year’s Pwn2Own was a first-come, first-served contest: The first researcher to hack each browser would win $10,000, but the second would take home nothing.
Nils also sidestepped DEP and ASLR in Windows 7 when he exploited the newest version of Firefox later in the day. Like Vreugdenhil, Nils also was awarded the notebook and $10,000. This was Nils’ second Pwn2Own victory; last year he grabbed $15,000 by exploiting not only Firefox, but also Safari and IE8.
“As usual, Nils’ exploit was very thorough,” said TippingPoint’s Portnoy, who is the organizer of the Pwn2Own contest.
TippingPoint purchased the rights to the flaws and attack code from Vreugdenhil, Nils and the other Pwn2Own winners. It will turn over that information to Microsoft, Mozilla and other affected vendors on Friday at the conclusion of the contest. Until vendors patch their vulnerabilities, TippingPoint will not disclose any technical information about the bugs.
Both Microsoft Corp. and Mozilla Corp. had representatives on hand during the contest.
Later, Jerry Bryant, a senior manager with the Microsoft Security Research Center (MSRC) acknowledged the vulnerabilities exploited by Vreugdenhil, but little else. “Microsoft is aware of a new vulnerability in Internet Explorer introduced at CanSecWest in the Pwn2own contest,” Bryant said in an e-mail Wednesday. “We are investigating the issue and we will take appropriate steps to protect customers when the investigation is complete.”
Bryant did not say when Microsoft would patch the flaws Vreugdenhil used. The company’s next scheduled Patch Tuesday is April 13, but Microsoft typically takes much longer to produce its fixes, with testing time alone often running 30 to 60 days.
The lesson from this year’s Pwn2Own is pretty simple, suggested Charlie Miller, another of Wednesday’s winners. “What you can see at Pwn2Own is that bugs are still in software, and exploit mitigations like DEP and ASLR don’t work. Even as [defensive measures] improve, researchers still end up winning.”