Microsoft last week issued a security alert to warn users of a bug in most versions of Windows, but didn't promise to fix the flaw or -- if it does patch the problem -- say when a fix would be released.

A little more than three weeks ago, Microsoft had denied that the problem was a vulnerability.

In a security advisory published on Thursday, Microsoft categorized the vulnerability as an "elevation of privilege" that, if exploited, could give attackers significantly greater access to the compromised machine. The bug affects Windows XP Professional SP2, and all versions of Windows Server 2003, Windows Vista and the brand-new Windows Server 2008.

Although the flaw is within Windows, attackers could conceivably exploit it through custom Web applications running in Microsoft's Web server, Internet Information Services (ISS). It could also be exploited via SQL Server, added Microsoft.

"Web apps usually run in a lesser-privileged mode," said Andrew Storms, director of security operations at nCircle Network Security. "[Using this vulnerability, attackers} could jump that privilege to a LocalSystem account, which is not a long way from an administrative account.

"You can do quite a bit with a LocalSystem account," Storms said.

Several weeks ago, Cesar Cerrudo, a researcher and security consultant based in Parana, Argentina, announced that he would disclose a Windows flaw at an upcoming conference. The vulnerability, Cerrudo said in late March, could let attackers bypass some of the security schemes in the newest versions of the operating system, including Windows Server 2008.

In a story posted by the SearchSecurity.com Web site, Cerrudo said that attacks could be launched through IIS, and that the threat could be mitigated by running Web applications under a different account from NetworkService, LocalService and LocalSystem.

At the time, Bill Sick, a spokesman for the Microsoft Security Response Center (MSRC), said that Cerrudo's information appeared to be about a "design flaw" rather than a true vulnerability. Sisk also downplayed the threat. "The presentation does not describe methods for an attacker to gain access to these trusted accounts," he told SearchSecurity.com.

Thursday, however, Cerrudo unveiled the vulnerability in a presentation at HITBSecConf2008, a security conference that opened Monday and wrapped up Thursday in Dubai, United Arab Emirates; Microsoft followed that presentation with its advisory.

Friday, the company confirmed that Cerrudo's findings prompted its advisory. "Yes, the security advisory released yesterday and presentation by a researcher in Dubai relate to the same issue," a company spokeswoman said in an e-mail.

As it often does in its advisories, Microsoft did not promise to create a patch. "Upon completion of this investigation, Microsoft will take the appropriate action to help protect our customers," Sisk said in a post to the MSRC blog. "This may include providing a security update through our monthly release."

But Microsoft rarely issues a security advisory without at some later date providing a patch, Storms noted.

The next scheduled release date for a Microsoft patch is May 13.