John Pescatore, Gartner's primary security analyst, agreed, but added, "If they want to stick with the index, they need to adjust the criteria so fewer vulnerabilities get a '1.'"
With vulnerability-by-vulnerability predictions correct only a fourth of the time, Storms questioned the usefulness of the exploitability index. "What's the point of the index if they're always going to side on the more risky side, as opposed to what's most likely?" he asked. "In some ways, we're back to where we were before they introduced the exploitability index."
From Storms' point of view, the exploitability index was meant to provide more granular information to customers who wondered what should be patched first. Presumably, a vulnerability marked critical with an index rating of "1" would take precedence over a critical vulnerability tagged as "2" or "3" on the exploitability index.
"With these numbers of false positives, we are in no better place than we were prior to the index, in respect to granularity," he said.
Pescatore also questioned the usefulness of the exploitability index. "I doubt anyone even looks at it," he said.
Instead, Pescatore again argued, as he did last year when Microsoft debuted the index, that the company would better serve customers by abandoning its own severity and exploitability rankings, and move to the standard CVSS [Common Vulnerability Scoring System] ratings. The CVSS system is used by, among other companies and organizations, Oracle, Cisco and US-CERT.
"Because Microsoft does its own exploitability index, enterprises can't compare theirs with Adobe's or Oracle's. It's an apples and oranges thing then," said Pescatore. "It's not just Windows bugs that companies have to deal with anymore."
He doubted Microsoft would take his advice. "They don't want to do that because then reporters and analysts can look and say, 'Microsoft has more higher-rated vulnerabilities than Oracle or Adobe,'" he said. "There's nothing in it for them to do that."
Microsoft made the right call on all 46 vulnerabilities that were assigned an exploitability rating of "2" or "3," which indicate that an exploit would be unreliable or unlikely, respectively. "None were identified to have been publicly exploited within 30 days," Microsoft's report noted.
If all its predictions in the first half of 2009 are considered, not just those marked as likely to be exploited, Microsoft got 57 out of a possible 87, or 66% of them, right.
Microsoft's security intelligence report, which covers the January-June 2009 period, was the first to spell out the accuracy of the exploitability index. But Microsoft has touted its forecasting before. A year ago, for example, Microsoft said in a postmortem of its first-ever index that although it had accurately predicted exploits less than half the time, it considered the tool a success . "I think we did really well," said Mike Reavey, group manager at the Microsoft Security Research Center (MSRC), at the time.
Microsoft's security intelligence report can be downloaded from its Web site in PDF or XPS document formats.