Exploit available for year's first critical Windows bug

Patch now, researchers urge; vulnerability has potential to be 'biggest of 2008'

A just-released proof-of-concept exploit against the year's first Windows vulnerability has security researchers ringing alarm bells.

Proof-of-concept code for the TCP/IP flaw spelled out January 8 in Microsoft's MS08-001 security bulletin was added to Immunity Inc.'s CANVAS penetration testing software on Wednesday. Thursday, Dave Aitel, Immunity's chief technology officer, warned that Microsoft may have overestimated the difficulty of creating a reliable exploit for the new bug.

"Microsoft makes triggering the issue sound a bit harder than it actually is," argued Aitel in a message to his Dailydave security mailing list on Thursday.

Last week, after Microsoft issued MS08-001 -- a bulletin that spelled out multiple vulnerabilities in Windows' TCP/IP protocols -- a Microsoft product manager writing in the new Security Vulnerability Research & Defense blog claimed that any attack would have to get lucky to successfully exploit the bug.

"Even though this bulletin is rated "critical" for XP and Vista, there are a number of factors that make exploitation of this issue difficult and unlikely in real-world conditions," argued Michael Grady, product manager in the company's Trustworthy Computing group.

Grady spelled out several factors that he said made an attack far-fetched, including an exploit chewing up most of the machine's CPU cycles and an attack requiring exquisite timing.

Aitel disagreed. "You'll be able to trigger it every time, especially on a local LAN," he said on Dailydave.

Others also expressed skepticism at Microsoft's estimate. "It's apparently possible to create a reliable exploit for this issue," Symantec Corp. told customers of its DeepSight threat network in a private research note. It then went on to say that even if creating an exploit is tough, the reward would be worth the work.

"An attack that potentially involves tens of thousands of packets to trigger may be difficult to reliably automate, [but] the payoff would be very high, since this has the potential to compromise numerous systems at once," Symantec continued.

Symantec also reminded customers that whenever a proof-of-concept appears, the likelihood of an in-the-wild attack climbs. "The emergence of [proof-of-concept] code (whether proprietary or public) is a reliable indicator of interest and focus on a particular vulnerability by both the attack and defense communities," Symantec said.

Some defenses previously cited as protecting users from MS08-001 attacks are, in fact, insufficient, Symantec added in a longer advisory issued to DeepSight clients. Windows XP's firewall, for instance, will not block broadcast attacks against the vulnerability, nor will other popular third-party consumer firewalls, such as the one included with Symantec's own Internet Security 2008 suite or McAfee's Internet Security Suite 2008.

Microsoft, which had dubbed the vulnerability as critical on both Windows XP SP2 and Windows Vista, patched the bug nearly two weeks ago. On Friday, Symantec urged users to deploy the fix as soon as possible.

Aitel, meanwhile, predicted that the TCP/IP flaw hammered by the CANVAS proof-of-concept exploit would get major play in the coming months. "I do think this vulnerability is going to be one of the biggest of 2008," he said on Dailydave.

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