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By | John Leyden 14th November 2007 09:32

Windows update offers defence against shell bug

Watch out, incoming

Microsoft released a critical patch involving IE7 and an important patch to guard against DNS (Domain Name System) spoofing on Tuesday.

An expected update involving a flaw in the SafeDisc copy protection software from Macrovision that comes bundled with Windows XP and 2003 is missing in action. Users are advised to apply Macrovision's update.

The light sprinkling of just two patches marks a relatively quiet month on the Patch Tuesday update treadmill. The most significant of the two updates addresses a URI (Uniform Resource Identifier) handling bug in Windows that could allow hackers to inject malware onto targeted systems.

Although the root cause of the problem stems from a bug deep in the Windows Shell, exploits doing the rounds require the installation of IE7. This security bug in the Windows Shell is exposed by applications including Outlook, Firefox, Adobe, and Skype. Exploitation involves the usual trick of fooling users into visiting maliciously constructed websites.

Systems running Win XP and Windows 2003 are potentially vulnerable. Those running Vista and Win 2000 are not. Attacks against vulnerable systems have been going on for some time.

The Internet Storm Centre describes the bug as a "well known problem with exploits in the wild". Vulnerable clients needed to be quickly patched, it advises.

The second of November's patches - described by Microsoft as important - involves a bug in Windows that might be exploited to poison a DNS cache.

The vulnerability stems from the use of predictable transaction values by Windows when sending out queries to upstream DNS servers. This creates a spoofing risk. More specifically, the bug allows hackers to send specially crafted responses to DNS requests, thereby spoofing or redirecting internet traffic from legitimate locations.

It's a fairly elaborate trick and there's no evidence, as yet, that hackers have pulled off the approach. Nonetheless ,users are advised to update Windows servers sooner rather than later.

Microsoft's summary of the patches can be found here. The Internet Storm Centre's more readable summary can be found here. ®

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