Microsoft is warning users of its Internet Explorer browser to use caution on the Web, after the disclosure of an unpatched bug that could allow attackers to seize control of a PC running the browser software.
The bug, disclosed Wednesday, relates to the way that IE processes information using the createTextRange() method. By presenting the browser with specially crafted code, attackers could corrupt the system's memory and trick it into running unauthorized software.
"We're still investigating, but we have confirmed this vulnerability and I am writing a Microsoft Security Advisory on this," wrote Lennart Wistrand, security program manager with the Microsoft Security Response Center, in a blog posting. "We will address it in a security update."
Microsoft's next scheduled set of security updates are due April 11, but Wistrand did not say whether the TextRange() bug would be patched then. Microsoft executives were not immediately available to comment for this story.
Wistrand offered IE users a work-around to avoid the problem. "Our initial investigation has revealed that if you turn off Active Scripting, that will prevent the attack," he wrote.
IE users with the latest refresh of the IE7 Beta 2 Preview software, announced this week are "not affected" by the problem, Wistrand said. Outlook and Outlook Express users are not at risk either, he added.
This is the third IE bug to be reported in recent days. The other bug, disclosed Tuesday, is also considered critical because it could also be used to seize control of a system. A third flaw, made public last Thursday, is considered less severe, but it can cause IE to crash.
The TextRange() method bug is considered the most serious of the three, however, because it appears to be relatively easy to exploit.
Wistrand's blog posting can be found here.