Microsoft patches final Pwn2Own IE bug

Quashed vulnerability that let researcher bypass browser's sandbox, win $15K in March

Microsoft on Tuesday patched the last vulnerability in Internet Explorer (IE) used by a researcher in March to win $15,000 at the annual Pwn2Own hacking contest.

The company had patched IE twice before to quash bugs exploited by Stephen Fewer of Harmony Security to bring down IE8 on Windows 7 at Pwn2Own. For his efforts, Fewer was awarded a cash prize of $15,000 and a Sony notebook.

Fewer chained three exploits, each for a different vulnerability, to bypass IE's sandbox, called "Protected Mode," and compromise IE8. Pwn2Own sponsor HP TippingPoint called the feat "impressive" at the time.

Microsoft patched the third IE bug in a multiple-flaw update to its browser, part of a 13-bulletin collection.

Although Microsoft credited Fewer in the MS11-057 bulletin for reporting the third vulnerability, it said the bug wasn't a security flaw. "Yes, this update addresses a Protected Mode bypass issue, publicly referenced as CVE-2011-1347," Microsoft said in response to an FAQ query, "Does this update contain any non-security related changes to functionality?"

At Pwn2Own, Fewer used the bypass bug to escape Protected Mode so he could circumvent the browser's sandbox, which allowed him to add a file to the machine, a task that mimicked a hacker's insertion of malware.

Fewer confirmed that yesterday's IE update fixed the final flaw he used at Pwn2Own.

"Yes MS11-057 patches the final bug, the protected mode bypass, that I used in my Pwn2Own exploit, the other two being a use-after-free which was patched in MS11-018 and an information leak patched in MS11-050," Fewer said today in an email reply to questions.

MS11-018 and MS11-050 were the designations of the April and June bulletins, respectively, that patched the two other vulnerabilities he reported to Microsoft via TippingPoint's bug bounty program.

According to Aaron Portnoy, manager of TippingPoint security research team and the company's Pwn2Own organizer, Tuesday's IE update wraps up patching for the 2011 contest.

During Pwn2Own, Microsoft said that IE9, the browser that launched shortly after Fewer's hack, did not contain the bugs he exploited.

Including Tuesday's update, IE9 has been patched twice since its March launch. Of the August bugs Microsoft acknowledged as security issues, one was reported by Fewer.

"Yes, I have been doing some research into IE9 and actually my first IE9 vulnerability was also patched this Tuesday as part of MS11-057," Fewer said, referring to a separate bug he was credited with this week.

That flaw, dubbed "CVE-2011-1964," was reported via TippingPoint to Microsoft in May, and was ranked critical for IE9 when run on Vista or Windows 7.

Fewer wouldn't commit to taking on IE9 at next year's Pwn2Own, but he left the door open to a repeat performance. "I don't have any plans as of yet for next year's competition, but if I have a few new bugs handy closer to the time, who knows?"

August's security updates, including MS11-057 for IE, can be downloaded and installed via the Microsoft Update and Windows Update services, as well as through Windows Server Update Services.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His e-mail address is gkeizer@computerworld.com.

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