On Thursday, new code was posted on the Internet that could exploit a flaw in unpatched Microsoft Host Integration Servers.
The exploit is part of Metasploit, a toolkit used by penetration testers and criminal hackers alike.
On Tuesday, Microsoft issued security bulletin MS08-059 to address the vulnerability detailed in CVE- 2008-3466. In its patch bulletin, ranked as critical, Microsoft said "this vulnerability could allow remote code execution if an attacker sent a specially crafted remote procedure call request to an affected system. Customers who follow best practices and configure the systems network architecture remote procedure call (SNA RPC) service account to have fewer user rights on the system could be less impacted than customers who configure the SNA RPC service account to have administrative user rights."
Apparently Microsoft knew of the exploit. To help system administrators prioritize the patches an "Exploitablity Index" was inaugurated with the October Patch Tuesday releases. Microsoft gave MS08-059 a 1 for having "for consistently functioning exploits". Other index ratings include 2 for "inconsistently functioning exploits" (of moderate concern), and 3 for vulnerabilities that are "unlikely to produce functioning exploits" (of least concern).