April showers brought May flowers, or at least that appears to be Microsoft's story on the issue of software security vulnerabilities.

One month after the software giant disclosed dozens of software vulnerabilities, then watched as malicious code and a new family of worms appeared to exploit those holes, Microsoft decided to take it easy in May. The company published just one bulletin on Tuesday, covering a single non-critical vulnerability in some versions of Windows.

The company has released a software patch and a security bulletin, MS04-015, describing a vulnerability in the Windows Help and Support Center (HSC). A problem with the way the HSC handles information in URLs could allow a remote attacker to run malicious code on vulnerable Windows machines, potentially giving them total control over compromised systems, Microsoft says.

HSC URLs, which use the host configuration protocol (HCP) and begin with "hcp://", link to help resources in Windows and are similar to normal URLs, which use hypertext transfer protocol (HTTP) and begin with "http://".

To take advantage of the hole, an attacker would have to trick Windows users into clicking on an HSC link that was embedded in a Web page or an e-mail message formatted in HTML. Once clicked, the attacker could open a Help window containing content of the attacker's choosing. However, the user would still need to interact with the attacker's Help page and perform other actions to complete the attack, Microsoft says.

Microsoft has issued updates for the 32- and 64-bit editions of Windows XP and Windows XP Service Pack 1, as well as 32- and 64-bit editions of Windows Server 2003. Windows NT, 2000 and 98 are not affected by the HSC vulnerability, according to Microsoft.

The low-key security warning stands in marked contrast to April, when Microsoft published four security bulletins: MS04-011, -012, -013 and -014. Those bulletins contained patches for 20 unique software vulnerabilities, including critical holes in Microsoft's secure sockets layer library and the local security authority subsystem service (LSASS), which is used to authenticate users locally and in client-server environments.

Malicious code to exploit those holes appeared within days of publication of the bulletins. A new worm, Sasser, was released on May 1 to exploit the LSASS hole and already may have infected over a million Windows machines worldwide.

Microsoft encourages customers to install the May update at their earliest opportunity, but cautions that doing so would disable some Windows features.
Citing its "defence in depth" strategy of securing its products, Microsoft says the MS04-015 patch removes a Windows XP feature that enabled Windows to automatically offer users the option of upgrading a DVD device driver because the feature exposed users to unspecified "malicious use".

Installing the May patch will also break a feature in the Windows "Found new hardware wizard" that transmits hardware profile information after the wizard runs.

Customers who install the patch will receive error messages when try to use those features, Microsoft says.