Microsoft confirms IE6, IE7 zero-day bug

Computerworld - Microsoft today confirmed that exploit code published last week can compromise PCs running older versions of Internet Explorer (IE), but said its security team has not yet seen any in-the-wild attacks.

The attack code, which was posted Friday to the Bugtraq security mailing list, affects both Internet Explorer 6 (IE6) and the newer IE7, Microsoft acknowledged. "Microsoft can confirm that the publicly available exploit code affects IE6 and IE7, not IE8," a company spokesman said in an e-mail reply to questions today.

IE6 and IE7 account for more than 41% of all browsers used worldwide, according to the most recent data from metrics firm Net Applications. IE8, meanwhile, has an 18.1% market share.

Over the weekend, Symantec researchers took note of the exploit code, but said that it was shaky. "The exploit currently exhibits signs of poor reliability, but we expect that a fully-functional reliable exploit will be available in the near future," the security company's analysis team said in an entry on a company blog Saturday.

According to Danish vulnerability tracking vendor Secunia, the flaw is in IE's layout parser, and could be exploited by hackers to hijack fully-patched Windows XP Service Pack 3 (SP3) machines. Secunia rated the vulnerability as "highly critical," its second-highest threat ranking.

Microsoft declined to answer questions about which versions of Windows are vulnerable. Windows Vista, for example, ships with IE7. Windows 7, however, relies on the unaffected IE8.

The company also declined to spell out plans for quashing the IE bug. "Microsoft is investigating new public claims of a possible vulnerability in Internet Explorer," the spokesman said, using boilerplate that the company regularly rolls out when it's asked about patching progress. "Once we're done investigating, we will take appropriate action to help protect customers ... [which] may include providing a security update through the monthly release process, an out-of-cycle update or additional guidance to help customers protect themselves."

Microsoft will issue its next scheduled security updates in a little more than two weeks on Dec. 8.

One security researcher said it's unlikely Microsoft will move fast enough to make that deadline. "Seeing as though they haven't even posted an advisory, and with the holiday this week, I'm doubting a Dec. 8 release," said Andrew Storms, director of security operations at nCircle Network Security.

More likely, said Storms, is that Microsoft will offer steps that IE6 and IE7 users can take to defend themselves.

On Saturday, Symantec recommended that users disable JavaScript in IE6 and IE7, a move that could stymie attacks, since the current exploit code requires JavaScript.

To turn off JavaScript, users should select the "Tools" menu in IE, then click "Internet Options," the "Security" tab and the "Internet" content zone. Next, click "Custom Level" and in the "Settings" box, click "Disable" under "Active scripting." Click "OK" in the current dialog box, as well as the next.

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