Original URL: http://www.theregister.co.uk/2011/12/21/win_7_bug_crash_risk/

A simple HTML tag will crash 64-bit Windows 7

0-day leaves kernel in the wrong iframe of mind

By John Leyden

Posted in Software, 21st December 2011 10:07 GMT

An unpatched critical flaw in 64-bit Windows 7 leaves computers vulnerable to a full 'blue screen of death' system crash.

The memory corruption bug in x64 Win 7 could also allow malicious kernel-level code to be injected into machines, security alert biz Secunia warns. Fortunately the 32-bit version of Windows 7 is immune to the flaw, which has been pinned down to the win32k.sys operating system file - which contains the kernel portion of the Windows user interface and related infrastructure.

Proof-of-concept code showing how to crash vulnerable Win 7 boxes has been leaked: the simple HTML script, when opened in Apple's Safari web browser, quickly leads to the kernel triggering a page fault in an unmapped area of memory, which halts the machine at a blue screen of death.

The offending script is just an IFRAME tag with an overly large height attribute. Although Safari is required to spark the system crash via HTML, modern operating systems should not allow usermode applications to bring down the machine. Microsoft is now investigating the vulnerability, which was first reported by Twitter user w3bd3vil, although the software giant is racing against hackers tracing the code execution path to discover the underlying vulnerability in Windows 7.

A video of the Safari-triggered crash along with the HTML PoC can be seen here. Other exploit scenarios might also be possible. ®