Following questions, Microsoft explains WMF decision

The vulnerability may have been created deliberately, says researcher

Following speculation that a widely publicised vulnerability in Microsoft's Windows operating system may have been created deliberately, an executive within Microsoft's security group has published a detailed explanation of how the vulnerability was introduced. His conclusion: the WMF (Windows Metafile) security bug, which first came to light last month, was not an intentional "back door" added to give Microsoft a secret way of gaining access to its customers' PCs.

"There's been some speculation that ... this trigger was somehow intentional," writes Stephen Toulouse, security program manager with Microsoft's security response center. "That speculation is wrong."

Toulouse's comment came after security researcher Steve Gibson speculated that Microsoft had intentionally included a known vulnerability in a graphics rendering component of its operating system.

"The only conclusion that can reasonably be drawn is that this was a deliberate back door put into all of Microsoft's recent editions of Windows," wrote Gibson, the founder and president of Gibson Research, in a posting to his web site last week. Gibson Research is based in Laguna Hills, California. "Why it was put in and who knew about it, and what they were expected to use it for ... we'll never know."

Toulouse says that Microsoft has been fielding customer questions on this topic, many of which he assumed to have been triggered by Gibson's post. "We had been looking into detailing the history anyway and some customer questions drove the idea to write it up," he writes. "We just wanted to make sure people had the history."

The vulnerability in question concerns the way that Windows processes WMF graphics files, which are used by computer-aided design programs. In the 1990s, Microsoft added a function to Windows, called SetAbortProc, that is used in processing these files. Because of a design error in the function, it can be used by hackers to take control of a Windows computer, Microsoft says. Microsoft fixed the error in a Windows patch, entitled MS06-001, released earlier this month.

Gibson had previously argued that because the SetAbortProc function could not be triggered by a correctly formed WMF file, it served no legitimate purpose, a claim that Toulouse disputed in his posting. In an interview, Gibson concedes that he had been in error on that point. "I was wrong about this," he says. "It is more complex than that, exactly as [Toulouse] explained in his posting."

Still, Gibson stands by his previous conclusion, arguing that Microsoft appeared to have intentionally changed the SetAbortProc function around the time of Windows NT to make systems vulnerable to the coding error. "The best way to characterise this is, it's intentionally designed code which, without question, enables back-door functionality," he says.

Toulouse declined to comment on this claim, but in his blog posting, he wrote that it is more difficult to exploit the vulnerability in the Windows 95 and Windows 98 operating systems.

Security researchers contacted by IDG News are skeptical of Gibson's theory. If Microsoft truly wanted to add a back door to Windows, there are better ways the company could have done it, says Cesar Cerrudo, chief executive officer of security research firm Argeniss in Parana, Argentina. "I don't think Microsoft would use that kind of back door," he says. "They don't need to do that, they could just build an exploit for some unfixed remote vulnerability on Windows."

Gibson says that, while he has no proof of Microsoft's motives, he believes that such a back door could have been created without malicious intent -- perhaps as a way for Microsoft to provide assistance to users, for example. "It would be a way for Microsoft to help people who had shut their computers down, security-wise," he says.