An executive from Microsoft's security group has denied any deliberate intent on part of the company in a recent OS vulnerability.

The move follows wide speculation that the WMF vulnerability in Windows may have been created deliberately. The executive argues that 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.

Positive denial

"There's been some speculation that this trigger was somehow intentional," wrote Stephen Toulouse, security programme manager with Microsoft's security response centre, "that speculation is wrong."

Toulouse's comment, posted late Friday, came after security researcher Steve Gibson speculated that Microsoft had intentionally included the 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 last week. "Why it was put in, who knew about it and what they were expected to use it for...we'll never know."

Toulouse said 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 wrote in an email interview. "We just wanted to make sure people had the history."

What's sexy about SetAbortProc?

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 recent update.

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 Monday, Gibson conceded the error: "I was wrong about this," he said. "It is more complex than that, exactly as Toulouse explained in his posting."

Wrong or right, question remains

Still, Gibson stood by his previous belief, 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 said.

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

Gibson said 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 said.