MS fixes WinNT patch RAS knock-out glitch

Cure was worse than the disease

As if hard pressed Windows sysadmins didn't have enough problems dealing with the effects of the Blaster worm, Microsoft has warned that an unrelated security fix it supplied to NT 4 users last month was faulty.

The security patch, issued in July and designed to guard against a potential DoS risk, causes Remote Access Services to fail when a system is rebooted after applying the patch, Microsoft has admitted.

Microsoft has released a revised patch that doesn't cause such disastrous side-effects while shoring up defences against what Redmond describes as a "moderate risk" vulnerability.

The bug Microsoft is trying to fix involves a flaw with a Windows NT 4.0 Server file management function that gives rise to a denial of service vulnerability. The affected function can cause memory that it does not own to be freed when a specially crafted, malformed request is passed to it. As a result, application passing an improperly validated request to the function could fail.

By default, the affected function is not accessible remotely, however applications installed on the operating system (Application servers or Web servers, though not IIS 4) that are available remotely may make use of the affected function.

The vulnerability can't be used to crash Windows NT 4 Server itself, according to Microsoft. Default installations of NT 4 are not vulnerable to a remote denial of service. Additional software that makes use of the affected file management function must be installed on the system to expose the vulnerability remotely. Because of these mitigating factors, Microsoft designates the flaw as only moderate - and not critical.

Microsoft's advisory explains the issue in greater depth. ®

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