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A 17-year-old bug in Windows will be patched by Microsoft in its latest security update.

The February update for Windows will close the loophole that involves the venerable DOS operating system.

First appearing in Windows NT 3.1, the vulnerability has been carried over into almost every version of Windows that has appeared since.

The monthly security update will also tackle a further 25 holes in Windows, five of which are rated as “critical”.

Home hijack

The ancient bug was discovered by Google security researcher Tavis Ormandy in January 2010 and involves a utility that allows newer versions of Windows to run programs that date from the DOS era.

Mr Ormandy has found a way to exploit this utility in Windows XP, Windows Server 2003 and 2008 as well as Windows Vista and Windows 7.

The patch for this vulnerability will appear in the February security update. Five of the vulnerabilities being patched at the same time allow attackers to effectively hijack a Windows PC and run their own programs on it.

As well as fixing holes in many versions of Windows, the update also tackles bugs in Office XP, Office 2003 and Office 2004 for Apple Macintosh machines.

The bumper update is not the largest that Microsoft has ever released. The security update for October 2009 tackled a total of 34 vulnerabilities. Eight of those updates were rated as critical – the highest level.

In January 2010, Microsoft released an “out of band” patch for a serious vulnerability in Internet Explorer that was being exploited online. The vulnerability was also thought to be the one used to attack Google in China.

Following the attack on Google, many other cyber criminals started seeking ways to exploit the loophole.

Also this week, a security researcher has reported the discovery of a vulnerability in Internet Explorer that allows attackers to view the files held on a victim’s machine.

Microsoft has issued a security bulletin about the problem and aims to tackle it at a future date. At the moment there is no evidence that this latest find is being actively exploited online.

In a presentation at the Black Hat briefings, Mark Dowd of IBM Internet Security Systems (ISS) and Alexander Sotirov, of VMware Inc. will discuss the new methods they’ve found to get around Vista protections such as Address Space Layout Randomization(ASLR), Data Execution Prevention (DEP) and others. Essentially they’ve figured out a way to hack Vista using Java, ActiveX controls and .NET objects to load arbitrary content into Web browsers.

What they are indicating is that they have revealed a fatal flaw in Windows Vista which potentially blows the OS wide open and in such a way that it cannot be fixed. The attacks themselves are not based on any new vulnerabilities in IE or Vista, but instead take advantage of Vista’s fundamental architecture and the ways in which Microsoft chose to protect it.

Many of the defenses that Microsoft added to Vista and Windows Server 2008 are designed to stop host-based attacks. ASLR, for example, is meant to prevent attackers from predicting target memory addresses by randomly moving things such as a process’s stack, heap and libraries. That technique is useful against memory-corruption attacks, but Dai Zovi said that against Dowd’s and Sotirov’s methods, it would be of no use.

“This stuff just takes a knife to a large part of the security mesh Microsoft built into Vista,” Dai Zovi said. “If you think about the fact that .NET loads DLLs into the browser itself and then Microsoft assumes they’re safe because they’re .NET objects, you see that Microsoft didn’t think about the idea that these could be used as stepping stones for other attacks. This is a real tour de force.”

They go on to imply the approach can also potentially be applied to other operating systems such as Windows XP and Mac OSX (but not with this specific technique).

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