MSN Messenger vulnerable through IE bug

Shortly after Microsoft admitted that its MSN Messenger instant messaging program has a bug that could disclose the names and e-mail addresses on a user's contact list, the company is being confronted with what seems to be a bigger hole.

A malicious Web site operator can hijack a user's MSN Messenger application and perform all tasks, including sending messages and personal files, according to a bulletin posted on the Bugtraq mailing list on Saturday and a warning issued by security software firm Finjan Software on Sunday.

To take over a user's MSN Messenger program, an attacker has to exploit a known hole in Internet Explorer by sending specially crafted code in an HTML e-mail or directing the user to a Web site that contains that code, according to the security advisories.

The Internet Explorer hole, known as the Document.Open() bug, was first discovered in December. Microsoft has yet to plug the hole. A patch was initially published late last week, only to be removed from the Windows Update service hours later, according to a message on Tom Gilder's Web site. Gilder wrote the Bugtraq bulletin.

Finjan expects the flaw to be exploited by many and states that an "MSN Messenger worm" could be written based on this vulnerability. MSN Messenger 2.21 and above on systems with Internet Explorer 5.5. and 6.0 installed are vulnerable, according to Finjan.

Users can protect themselves by disabling active scripting in Internet Explorer or by not using MSN Messenger, which is software offered for free by Microsoft and is a standard part of Windows XP.

Microsoft on Friday confirmed that MSN Messenger has a bug that could disclose the names and e-mail addresses on a user's contact list to malicious Web site operators. The company is working on an update for MSN Messenger to fix that flaw.

Nobody at Microsoft was immediately available for comment.

The IDG News Service is a Network World affiliate.