Zero-day Windows bug problem worse than first thought, says expert

'Most every Windows application' at risk, says Slovenian security firm that's working with Microsoft on fix

An unpatched problem with Windows applications is much worse than first thought, with hundreds of programs, not just 40, vulnerable to attack, a Slovenian security company said today.

"It was a shocking surprise," said Mitja Kolsek, CEO of Acros Security. "It appears that most every Windows application has this vulnerability."

Yesterday, American researcher HD Moore announced that he had stumbled upon about 40 Windows applications with a common vulnerability, but he declined to name the programs or go into detail about the bug.

Today, Kolsek said that Acros has been digging into a new class of vulnerabilities for months. It has found more than 200 flawed applications harboring more than 500 separate bugs, he added, noting that the company had reported its findings to Microsoft more than four months ago.

In other words, the problem is much more widespread than Moore suggested on Wednesday.

"We examined a bunch of applications, more than 220 from about 100 leading software vendors, and found that most every one had the vulnerability," said Kolsek. Acros built a specialized tool to help its researchers pinpoint which applications were vulnerable.

According to Kolsek, the bug is in the way most applications load and execute code libraries -- ".dll" files in Windows -- and executables, including ".exe" and ".com" files. He dubbed the class of bugs as "remote binary planting," and said the flaws could be easily exploited.

"The main enabler for this attack is the fact that Windows includes the current working directory in the search order when loading executables," he said. Hackers can use that to trick a wide range of Windows applications into loading malicious files, just as they normally do their own .dll or .exe files.

Many Windows applications rely on the functionality to operate, a problem that may prevent Microsoft from issuing a single patch. Although Microsoft could patch Windows to change the functionality, Kolsek at one point said he believed that such a fix could break scores of applications.

Later in the interview, however, Kolsek seemed to waffle. "I'm very confident that Microsoft will come up with a solution that will work fairly well for most people," he said. "But it's not going to remove the problem."

If Microsoft doesn't come up with a fix, application vendors may have to issue separate patches, a stance that Moore, the CTO of Rapid7 and creator of the open-source Metasploit penetration testing tool kit, took Wednesday. Another option may be for Microsoft to issue an update targeted at developers, who would then use it to patch their own code -- a tactic Microsoft used two years ago when it addressed a bug in the ATL (Active Template Library) code library.

Kolsek also said that he thought Microsoft would have some kind of solution sooner rather than later. "They'll do something very quickly," he said. He added that he wasn't privy to Microsoft's schedule.

One clue to a possible patch schedule is that Kolsek is slated to present a paper on remote binary planting at the DeepSec security conference, which is set to take place Nov. 23-26 in Vienna, Austria. Because Acros and Microsoft have been in discussions about the vulnerabilities, one could assume any Microsoft-generated fix would ship before Kolsek steps on stage this fall.

Kolsek hinted today that Acros and Microsoft had intended to keep the problem under wraps for a little bit longer.

"But now that the cat is out of the bag," said Kolsek, referring to Moore's disclosure Wednesday, there was no reason not to go public with a bare-bones description of the problem.

That problem could be even bigger than Acros has pegged it, Kolsek admitted.

"We calculated that there are about 100 billion instances of this class currently exposing users," he said, explaining that Acros came up with that number by assessing the market share of individual applications that contain the bug and then multiplying it by the global installed base for Windows.

"These vulnerabilities' critical impact and relative ease of exploitation present a serious threat to basically all Windows machines," Kolsek said.

Acros plans to publish more information on the vulnerability class soon.

Microsoft declined to comment further about the vulnerabilities, and instead referred to a statement it provided Computerworld earlier today, in which it confirmed it was investigating.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, or subscribe to Gregg's RSS feed . His e-mail address is

Copyright © 2010 IDG Communications, Inc.

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