Microsoft's latest patch needs patching

Antivirus specialist GeCad Net is warning that it has found a problem with Microsoft's most recent software patch for Windows.

The Romania-based security service provider said that a critical patch issued by Microsoft in its MS05-001 bulletin earlier this month fails to resolve all of the security issues surrounding the HTML Help ActiveX control in Windows. Microsoft distributed the fix, along with additional security updates, to address the threat of attackers placing and executing malicious programs such as spyware on affected computers.

GeCad, which sold its antivirus software business to Microsoft in 2003, said that the patch has not addressed at least one so-called attack vector, or weakness, that could allow an exploit of the HTML Help ActiveX control vulnerability.

A Microsoft representative said on Monday that the company is already working to close the loophole reported by GeCad, and emphasised that the January patch had fixed the original reported problem.

"Microsoft issued an update to address a vulnerability in the HTML help control in Windows, and this update does protect against the publicly reported vulnerability," the representative said.

Moreover, the software maker disagreed that it overlooked a potential exploit with its patch. Instead, it said that the problem is a new flaw in HTML Help control that was not tackled in the update.

"Microsoft has been made aware of a publicly reported exploit of a different vulnerability than the one addressed," the representative said. "This vulnerability could be exploited in such a way as to cause the HTML Help control to execute code on a user's computer."

Microsoft did not say whether the fix would be released before its February patch bulletin.

GeCad said it is not disclosing technical details of the attack method right now for "security reasons". Microsoft has butted heads with security researchers in the past when they have disclosed information about flaws before the company has been able to patch them.

The antivirus company said the potential for attack is opened up if a computer is updated with Microsoft's Windows XP Service Pack 1 or Windows 2000 Service Pack 4, along with the most recent security patches. It also noted that updating with Microsoft's Windows XP Service Pack 2 seems to prevent the problem.

In 2003, Microsoft purchased GeCad Software, GeCad's antivirus software development business, but the remaining company continues to operate as a security researcher and consultancy. Microsoft is expected to release its own antivirus software sometime later this year.

Matt Hines writes for CNET News.com.