A vulnerability has been discovered in Microsoft Windows that allows hackers to remotely access PCs and install malware through an imaging-handling technology in the operating system.
Microsoft acknowledged the release of exploit code that could allow an attacker to execute arbitrary code when someone visits a Web site that contains a specially crafted Windows Metafile (WMF) image. Security authority Secunia labelled the vulnerability "extremely critical."
WMF images are graphical files that can contain both vector and bitmap-based picture information. Microsoft Windows contains routines for displaying such files, but a lack of input validation in one of these routines may allow a buffer overflow to occur, which in turn may allow remote code execution.
The vulnerability can also be triggered from the Internet Explorer (IE) browser if the malicious file has been saved to a folder and renamed to other image file extensions such as .jpg, .gif, .tif, and .png. It has been detected on a patched system running Microsoft Windows XP SP2. Microsoft Windows XP SP1 and Microsoft Windows Server 2003 systems also are affected.
Current exploits use the Windows Picture and Fax Viewer to attack any application that can handle Windows Metafiles. Disabling the Windows Picture and Fax Viewer will not eliminate the risk as the flaw exists in the Windows Graphical Device Interface library.
The flaw has also raised concerns that Google Desktop may be another potential attack vector, and that various anti-virus software products cannot detect all known exploits for this vulnerability.
By default, Explorer on those operating systems runs in a restricted mode known as Enhanced Security Configuration, which Microsoft said mitigates this vulnerability as far as e-mail is concerned, although clicking on a link in a message would still put users at risk.
Yankee Group senior analyst Andrew Jaquith characterised the vulnerability as a serious security issue that has cropped up before in browsers, including Firefox and Safari. "It's particularly nasty because the browser automatically loads images when users visit a Web site. There is no built-in protection," he said.
Jaquith predicted that additional exploits of the vulnerability are expected since there is no patch available and the security hole is difficult to plug. People who use Windows are advised to be wary when opening e-mail and links in e-mail from sources they don't trust. They should not save, open or preview image files from unfamiliar sources. And, as always, people are encouraged to update the patches for their operating systems.