Updated Microsoft released four patches - all rated important - as part of its regular Patch Tuesday update cycle, one of which left ZoneAlarm users locked out the internet.
The most significant of the quartet fixes a flaw in Windows' implementations of the Domain Name System protocol (MS08-037.mspx). Multiple vendors are subject to the DNS-spoofing vulnerability, which stems from a fundamental weakness involving a lack of entropy in DNS queries rather than a specific security bug. Successfully exploiting the flaw could allow hackers to spoof DNS replies, creating a means to redirect network traffic or to mount man-in-the-middle attacks.
Unfortunately Microsoft's fix creates problems in itself, leaving users of the popular ZoneAlarm firewall unable to access the internet after they apply the patch.
The experiences of Reg reader Steve seem typical. "I woke up this morning to no internet at all and on calling my ISP's tech support I was told there was an issue with the latest patches and Zone Alarm," he reports. "I have uninstalled Zone Alarm and everything now works fine. Not sure who is to blame on this one but it has been a pain."
ZoneAlarm has published a list of recommended workarounds to dealing for the glitch here.
Microsoft's three other patches cover vulnerabilities in Exchange server and SQL Server and, on the desktop, bugs in Windows Explorer. The Explorer vuln potentially creates a means for hackers to inject malware onto vulnerable systems running Windows Vista. This flaw - along with cross-site scripting vulnerabilities in Outlook for Web Access that affect MS Exchange and information disclosure bugs in SQL Server - are all rated "important" by Redmond but "critical" by security watchers at the SANS Institute's Internet Storm centre.