Microsoft released 11 security updates yesterday, including fixes for critical security bugs in Windows Active Directory, Internet Explorer, Excel and the Microsoft Host Integration Server, which integrates Windows computers with IBM mainframes.
Security experts say that the Internet Explorer update, which fixes six bugs in the browser, is the one to watch. That's because it is rated critical for Internet Explorer 6 users running Windows XP - a very common configuration.
But customers who are running Windows Active Directory on older Windows 2000 machines should move the MS08-060 Active Directory update to the top of their patch queue, said Don Leatham, a director of solutions and strategy at Lumension Security. Because an Active Directory server can be used to set permissions on other machines and manage users on the network, taking over this machine "would be the Holy Grail for someone trying to get into a company and totally disrupt it", he said.
Normally, Active Directory servers are blocked at the firewall, which means that an attacker would probably have to be on an internal network to mount an attack, said Eric Schultze, chief technology officer with Shavlik Technologies. But the bug "means any internal, disgruntled user can take complete control over Windows 2000 domains and domain controllers", he said.
Mitigating this concern, however, is the fact that Microsoft has not had any reports that this vulnerability has been exploited in an attack. While it's likely that an attacker could crash the Windows 2000 machine by exploiting this bug, "creating functioning exploit code to leverage remote code execution is difficult," Microsoft said in a note on its website.
In total, 20 security bugs were fixed in Microsoft's 11 updates. There were also six less-critical updates, rated 'important', by Microsoft, for various Windows components, and a 'moderate' patch that fixes a bug that could let an attacker snoop information from an Office user.