On Thursday, Microsoft issued a rare out-of-cycle patch for a VULNERABILITY in the Windows Server service that HANDLES REMOTE procedure calls (RPC) that allows programmers to run code either locally or remotely. In issuing MS08-067, Microsoft warns "it is possible that this vulnerability could be used in the crafting of a wormable exploit." Entitled "Vulnerability in Server Service Could Allow Remote Code Execution (958644)" the specific vulnerability has been assigned a National Vulnerability Database designation of CVE-2008-4250.

Microsoft rates this patch as critical for Microsoft Windows 2000, Windows XP, Windows Server 2003, and important for Windows Vista and Windows Server 2008. It also affects versions of Windows 7 pre-beta in limited release. The patch replaces MS06-040.

Microsoft normally issues patches on the second Tuesday of each month, which has been deemed Patch Tuesday. But out-of-cycle patches are not without precedent. Recent examples include the Windows Animated Cursor Remote Code Execution Vulnerability (April 2007), a vulnerability in Vector Markup Language (September 2006), and a vulnerability in the Graphics Rendering Engine (January 2006).

Microsoft said there have been only limited and targeted attacks to date.

The company did say that a firewall should block network resources from attacks from outside the enterprise perimeter.

The patch is available via Microsoft Update or the individual bulletin for MS08-067.