The scope and simplicity of the Microsoft Outlook bug we reported last week is far more serious than we first suspected.
On Friday we reported that veteran bug hunter Georgi Guninski had discovered a loophole with Office XP which might allow an attacker to view a victim's email, delete or manipulate his or her data.
This is bad enough but Microsoft has now been forced to concede the potentially devastating vulnerability affects not only Office XP but also Office 2000 and 98 to boot. The software giant has admitted that an attacker might be able to run malware of his choice simply by tricking a victim into visiting a maliciously constructed Web site.
The root cause of the problem is an ActiveX feature, called Outlook View Control, which allows Outlook mail folders to be viewed via Web pages. Microsoft meant to design this feature so that data could only be browsed, but in practice it exposes a function that could allow an attacker to "delete mail, change calendar information, or take virtually any other action through Outlook including running arbitrary code on the user's machine".
Either maliciously constructed script or HTML code could allow a hacker control of a machine and attacks could be mounted either from a Web page or by tricking a user into opening a poisoned HTML email.
Guninski, who has a history of clashing with Microsoft over the speed at which it responds to his alert, has produced a demo of the bug. Ironically those curious enough to test this bug might be prompted by a security warning asking if they want to install and run the offending Microsoft Outlook View Control component. Don't all rush at once...
Microsoft is preparing a patch to shore up Outlook's defences against the bug and, in the meantime, has advised e-mail Outlook 98 and 2000 users to install the Outlook E-mail Security Update if they haven't done this already.
Some security firms, such as Finjan Software, are advising clients to restrict their use of ActiveX controls, and calling on Microsoft to take away lessons from a exploit that lower the bar on how difficult it is to take over a user's machine. ®