The software vendor also issued the second and third bulletins of 2003 at the same time. Bulletin MS03-002 details a flaw in Content Management Server 2001 rated "important" and MS03-003 offers a patch for a "moderate" vulnerability in Outlook 2002.
The "critical" flaw lies in the Microsoft Locator service, software used to map easy-to-remember logical names of systems on a company's network, such as a print server, to the actual network addresses, Microsoft said in security bulletin MS03-001.
By default, the Locator service is enabled only on Windows 2000 and Windows NT 4.0 server configurations used as domain controllers. It is not enabled on Windows NT 4.0 workstations or servers, on Windows 2000 workstations or servers, or on Windows XP.
An attacker could take over a vulnerable system by sending a malformed request to the Locator service. However, a firewall set to block external NetBIOS traffic would prevent attacks from the Internet.
Nevertheless, Microsoft urges all users of the affected operating systems to apply the available software patch. Administrators of Windows 2000 and Windows NT 4.0 domain controllers should apply the patch immediately.
Users can check to see whether the Locator service is running on their system by typing "net start" at the command line. The Locator service is running if the entry "Remote Procedure Call (RPC) Locator" appears in the displayed the list of services.
The second bulletin, MS03-002, details a serious flaw in Content Management Server 2001, a product used to build and manage Web sites. It contains a flaw that could allow an attacker to intercept data that an Internet user shares with a site created using the Microsoft software and alter the data shown to the user.
The third bulletin discusses a flaw in the way Outlook 2002 handles V1 Exchange Server Security Certificates for e-mail encryption. As a result, Outlook does not correctly encrypt mail when such certificates are selected and sends plain text messages instead of secured messages.
Microsoft changed the way it rates security issues late last year. Under the new system, only vulnerabilities that could be exploited to allow malicious Internet worms to spread without user action are now rated critical.
Many issues previously rated critical are now rated as "important". These "important" vulnerabilities could still expose user data or threaten system resources.