Microsoft is downplaying the threat posed by one of the three bugs the company patched today, said security researchers.

The update in question, MS11-035, patches a single vulnerability in WINS (Windows Internet Name Service), a component in every supported edition of Windows Server, including Server 2003, 2008 and the newest, Server 2008 R2. Attackers could exploit the WINS bug by crafting a malicious data packet, then shooting it at a vulnerable Windows Server box.

What irked researchers is that although Microsoft rated the bug as "critical," the company's highest threat ranking, it also pointed out that WINS is not installed by default, citing that as a mitigation factor. While true, that overlooks the fact that many networks, especially larger ones in enterprises and government agencies, have WINS installed.

"Most organisations have to install WINS," said Marcus Carey, Rapid7's enterprise security community manager. "With governments and big agencies, any large network, WINS is going to be running."

That's because WINS, Microsoft's name server for Windows networks, is required for many older third party or custom-built applications, called "legacy" programs, said Andrew Storms, director of security operations at nCircle Security. "There's so much legacy that relies on WINS [that] our gut instinct is that most will have it installed in the data centre," said Storms.

Like Carey, Storms said Microsoft, intentionally or not, softened the warning by telling customers WINS isn't installed by default. "They seem to be downplaying it," Storms said. "It is a network-based remote code possibility, so it comes with some trepidation."

Jason Miller, the data and security team manager for Shavlik Technologies, agreed. "There are more networks with WINS than most people think," he said. "Not only do some very old legacy applications require it, but some admins, those who inherited a network or those with less tech savvy, may not even know it's installed."

Because Microsoft last patched WINS in 2009, it's possible that the component is active without admins knowing it, Miller argued. One researcher, however, said Microsoft wasn't downplaying the WINS bug.

"Yes, the vulnerability is remote code executable," said the manager of Qualys' vulnerability research lab. "But I don't think they're trying to downplay it. WINS is not really needed anymore, unless you have some really old software, like SQL Server 2000."

Carey, Storms, Miller and Sarwate all believe that attackers will focus on the WINS vulnerability. "This is a big deal," said Carey. "There's not an active exploit for this as far as we know, but if attackers are on the top of their game, they could have one in a week or less."

Carey said that hackers could use fuzzers, tools that hammer at an application looking for a weakness, to quickly locate the flaw in WINS. "We think it will be easy to do, and that they'll figure it out quickly," he said.

The most likely attack would not be against a Windows Server directly, but against a desktop or notebook PC within the network, Carey continued. "They could exploit a client [with another vulnerability] then pivot the attack to the server," he said. Once a hacker compromised a Windows Server system, he could pillage the machine for confidential information, account log-in credentials and the like.

"I think this will be packaged with a number of other vulnerabilities," said Miller, talking about the possible use of the flaw. "Servers are a prime target."

Microsoft urged network administrators to patch the WINS vulnerability as soon as possible.

"The nice thing is that this is a light month," said Miller. "It should give everyone a chance to get ahead of the game."