The critical flaw, in the way Windows Meta File images are handled, is different than any security vulnerability the software maker has dealt with in the past, Kevin Kean and Debby Fry Wilson, directors in Microsoft's Security Response Center, said in an interview with CNET News.com. Typical flaws are unforeseen gaps in programs that hackers can take advantage of and run code. By contrast, the WMF problem lies in a software feature being used in an unintended way.
In response to the new threat, the software company is pledging to take a look at its programs, old and new, to avoid similar side effects.
What's new:
Microsoft plans to scour its code to look for flaws similar to a recent serious Windows bug and to update its Security Development Life Cycle process to prevent similar problems.
Bottom line:
The new species of flaw creates a new twist in Microsoft's battle with hackers, as it works to improve its security practices.
"Now that we are aware that this attack vector is a possibility, customers can be certain that we will be scrubbing the code to look for any other points of vulnerability based on this kind of attack," Fry Wilson said.
Microsoft has been working for years to improve its security posture, beginning with its Trustworthy Computing Initiative, launched in early 2002. The WMF problem is not a good advertisement for Microsoft's security efforts, one analyst said, as the legacy issue seemingly went undetected.
"This should have been caught and eliminated years ago," Gartner analyst Neil MacDonald said. "They overlooked image format files, and that is where this WMF issue came in."
Microsoft now faces a race with cybercriminals, who are likely on the prowl for the same bugs as well, experts said. The software maker is in a constant battle with miscreants who seek to attack computer users.
When WMF files were designed in the late 1980s, a feature was included that allowed the image files to contain computer code that could be executed on a PC, said Mikko Hypponen, chief research officer at Finnish security company F-Secure.
"This was not a bug; this was something that was needed at the time," Hypponen said. "It is just bad design, design from another era." The graphics file format was introduced with Windows 3.0 in early 1990. Executable code in the image file could help abort the processing of large images on the slow systems of yesteryear, security experts said.
Ilfak Guilfanov, a European software developer who made headlines by beating Microsoft to the punch with a fix for the Windows flaw, agreed. "WMF was designed a long time ago, when information security was not considered an essential part of software design," he said.
Trojan horses, instant messaging worms and thousands of Web sites were found to attack users with specially crafted WMF files. A vulnerable Windows computer might have been compromised simply if the user visited a Web site that contained a malicious image file, or opened such a file in an e-mail message or an Office document.
Many of the attacks installed spyware or other unwanted programs on the PCs of unwitting Windows users. At least a million computers were compromised, according to Andreas Marx, an antivirus software specialist at the University of Magdeburg in Germany. The WMF issue is also expected to be a conduit for many future threats, experts have said.
Response speed
Microsoft's fix for the flaw was the quickest turnaround ever for a Microsoft patch, released only 10 days after the vulnerability was made public, Fry Wilson said.
While Microsoft was able to repair the problem in record time, the company was surprised by the type of vulnerability.
"It is not a common buffer overflow," Kean said. "The software has a behavior that people can take advantage of. Obviously we did not intend it to be used in that way."
Microsoft has learned from the WMF flaw and will put the lessons into practice, Fry Wilson said. The software maker will update its Security Development Life Cycle, a set of practices that Microsoft's developers follow to prevent security vulnerabilities in products. The process includes the software maker's threat-modeling system, which checks code for potential security problems.
"This kind of threat has not been anticipated before," Fry Wilson said. "We will be revising that information in the SDL process and redoing the threat-modeling system to make sure we are looking for this kind of attack or anything similar to it."
Microsoft should have already been hunting for this type of design problem, MacDonald said. "I would have expected the SDL to already include data file formats. It should be a basic part of any security life cycle," he said.
As part of its development process, Microsoft looks for a number of common mistakes developers can make. These mistakes can turn into security problems and allow attackers to hijack a PC. Some of the common problems the company looks for are buffer overflow, integer overflow and stack overflow, Kean said.
The SDL is updated every six months. Microsoft now has a team that looks at issues as they come up, which it did not have a couple of years ago. By keeping its security processes current, the software maker aims to avoid the need to reassign substantial developer resources to an all-out security review, a company representative said.
Ferreting through its code and adapting its development practices is the right thing for Microsoft to do, several security experts said. "Microsoft has to become more proactive in finding and fixing these holes," said Johannes Ullrich, the chief research officer at the SANS Institute.
Mike Murray, director of vulnerability and exposure research at nCircle, a vulnerability management company in San Francisco, agreed. "That's the only step they can really take," he said. "Because this is a new thing, it is going to be something that a lot of bug hunters, both the good guys and the bad guys, will look for."
Microsoft doesn't expect to find many issues similar to the WMF problem, Kean said. "I don't expect this to be common, but it is something that we are going to look for," he said.
Guilfanov disputes that the WMF issue is something completely new, but agrees that the problem likely is an isolated one. "Nothing is really new under the sun," he said. "It is a design flaw. There shouldn't be many, but a code review can't hurt."
The WMF issue is similar to problems with Office files in the past, Guilfanov said. "The code-in-data concept is very powerful, but can bite back if not used with great care," he said. "A control mechanism should be available to disable execution of embedded code. A similar control played a great role in alleviating the Word Macro virus issue."
Vulnerabilities in file format handling are increasingly being uncovered. That's because image formats are complicated, and applications have to support many image file types, experts have said. This has opened new ways for attackers to target computers.
The hunt for other flaws in the new species of bug is on. For example, security provider F-Secure is looking to see if Windows Mobile software is vulnerable to the WMF flaw. Hypponen said he isn't sure whether Microsoft will find many design flaws like it: "I hope they don't, but I'm not holding my breath."
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