It's been a bad week for Internet Explorer users as the second potential devastating vulnerability in as many days has been discovered by security researchers.
Flaws in the way IE renders binary attachments in HTML email could be used to trick users into running malicious code on their machines, Microsoft has admitted.
The problem, which affects IE 5.5 and 5.01, stems from the way the browser processes certain unusual MIME types, which it handles incorrectly.
If an attacker created a HTML email containing an executable attachment, then modified the MIME header to indicate a type that IE handles incorrectly then the attachment would be launched automatically.
The vulnerability, which was discovered by Juan Carlos Cuartango, could be exploited through either coaxing a victim into browsing a maliciously-constructed Web site or via the opening of an infected HTML email.
In a security notice on the subject, Microsoft admitted: "This vulnerability could enable an attacker to potentially run a program of her choice on the machine of another user. Such a program would be capable of taking any action that the user himself could take on his machine, including adding, changing or deleting data, communicating with web sites, or reformatting the hard drive."
Microsoft has issued a patch to address the problem, which is available here.
Earlier this week another potentially nasty IE flaw was suggested by veteran bug hunter Georgi Guninski.
In an advisory, Guninski said that the way Microsoft's Internet Explorer (IE), Internet Information Server (IIS) and Exchange 2000 work together can be exploited to obtain access to either server directories or email.
The issue is quite complex and concerns the way the scripting interface for accessing and manipulating object on IIS 5.0 or web storage (a feature of Exchange 2000) works.
Microsoft are looking into the issue and are reportedly not pleased with Guninski's early disclosure of a possible bug. In an email to Guninski, the software giant suggested any possible flaw could be effectively guarded against by using the trusted zones feature in its software.
Richard Stagg, a security consultant at Information Risk Management, said Guninski appeared to have hit on a live issue but he added that the more important factor was whether a packaged exploit would emerge, and that remained unknown. ®