Microsoft last week attached a health risk to one its own security patches, following widespread complaints that the fix slowed systems to a crawl.

The problematic patch, designed to fix a flaw in the way the kernel passes error messages to a debugger, was issued on April 16. The vuln affects Windows NT 4.0, NT 4.0 Server, Terminal Server Edition, Windows 2K and Windows XP) and is - potentially - very serious. However the vuln is also difficult to exploit, hence Microsofts designation the problem as "important" - and not critical.

For an attack to be successful, an attacker would need to be able to logon interactively to the system, either at the console or through a terminal session, Microsoft explains. Servers are less vulnerable to the issue, according to MS, because of commonplace restrictions on the ability to logon interactively.

Once this substantial login hurdle is cleared, all manner of mischief is possible.

"An attacker could exploit this vulnerability to take any action on the system including deleting data, adding accounts with administrative access, or reconfiguring the system," according to Microsoft.

XP users who followed Microsofts initial advice and applied the patch were in for a nasty surprise.

Reg reader Granville Gough writes: "If you are running WinXP and install this fix, your machine will be compromised. It will slow to a crawl, taking up to 30 seconds to open a spreadsheet, Word doc, run Meidaplayer and more."

"The problem goes away if the fix is removed," he adds.

In a warning, issued on Friday, (Apr 25) Microsoft says it has "investigated this issue and confirmed that there can be performance problems when the patch is applied to Windows XP Service Pack 1 systems.

"Microsoft is actively working on a revised patch for Windows XP Service Pack 1 and will re-issue that patch when it has been completed and fully tested."

However reader Scott Lappin reports that the flaky patch also had "disastrous effects" on Win2K systems, so it seems the performance problems are not isolated to WinXP - contrary to Microsofts suggestion.

So until Microsoft gets its act together users are left with the choice of leaving their systems vulnerable to an "important" security flaw or applying an exceedingly slow quick fix.

Microsofts revised advisory fails to clearly recommend either course of action, leaving it to the discretion of users.

Source: The Register