Internet Explorer has become an even bigger security risk – even under Windows XP SP2 – with the publication of a new and extensive exploit.
Security researchers have warned that the exploit, which takes advantage of known loopholes in SP2, could allow an attacker to run script code on a user's system via a specially crafted web page.
The holes involved have been known publicly for more than two months, but previous exploit techniques required the victim to take actions such as dragging an image from one part of a web page to another.
The new exploit – a demonstration of which has been published by Danish security firm Secunia – is fully automated, requiring the user only to visit a web page in Explorer. Other browsers and operating systems aren't affected. Secunia has raised its warning level to its highest, "extremely critical."
Security group Greyhats warned of the new type of exploit in an advisory in late December. Secunia then upgraded its advisory to "extremely critical" and published a demonstration based on a proof-of-concept by a researcher known as ShredderSub7. US-CERT, the US computer security alert organisation, has also published an advisory on the issue.
Microsoft has warned users to turn off IE's 'Drag and drop or copy and paste files' option as a partial solution. The danger can also be lessened by setting security levels to high for the 'internet' zone or, as several security firms pointed out, using another browser.
The exploit is the first major weakness in SP2 to have surfaced. Microsoft is promoting SP2, released last summer, as a solution to many of Windows' worst security problems.
Researchers have identified three separate but related issues in IE: a bug in the validation of certain drag-and-drop events, and zone restriction errors with embedded HTML Help ActiveX controls. The first problem can be avoided by disabling the 'Drag and drop or copy and paste files' option, but the new exploit doesn't rely on this particular bug, researchers said.
The HTML Help control exploit bypasses one of SP2's key features, the 'Local Machine' zone lock down, designed to make it far more difficult for attackers to execute script on a local system.