"The Internet Explorer team accelerated testing of this update due to the growing attacks against the publicly disclosed vulnerability (CVE-2010-0806), and the update has reached the appropriate quality bar for distribution to customers," said Microsoft Security Response group manager Jerry Bryant in a blog post. "Releasing the update early provides Internet Explorer 6 and 7 customers protection against the active attacks and provides users of all versions of Internet Explorer protection against nine other vulnerabilities."
Symantec security researcher Joshua Talbot said in an e-mail that the catalyst for the patch is the increased activity related to the iepeers.dll zero-day vulnerability that surfaced March 9. "Symantec has also observed a recent spike in attempted infections via this security hole," he said. "The typical attempted infection process seems to involve compromising a legitimate Web site then inserting an iframe which redirects users to a malicious site."
Internet Explorer 6 and 7 users are at risk from the iepeers.dll vulnerability; Internet Explorer 8 users are not.
However, three of the other 10 vulnerabilities addressed by the out-of-band patch do affect Internet Explorer 8. Even so, Microsoft is urging customers using Internet Explorer 6 and 7 to upgrade to version 8.
Talbot says that while exploit code for the vulnerabilities other than iepeers.dll isn't yet available, he believes many of the holes will be "trivially exploitable under certain circumstances" and advises patching as soon as possible.
Bryant says that Microsoft cannot immediately provide information about whether the patch addresses the vulnerability used to hack Internet Explorer 8 in the "pwn2own" competition at the CanSecWest security conference last week.
The last time that Microsoft released an emergency patch for Internet Explorer was in January, following news that a vulnerability in Internet Explorer 6 had been used in the "Operation Aurora" cyber attack on Google and dozens of other companies.