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Microsoft's exploit predictions are right less than half the time

'We did really well,' company says; others doubt usefulness of rating system

November 12, 2008 12:00 PM ET

Computerworld - Microsoft Corp. today called its first month of predicting whether hackers will create exploit code for its bugs a success -- even though the company got its forecast right less than half the time.

"I think we did really well," said Mike Reavey, group manager at the Microsoft Security Research Center (MSRC), when asked for a postmortem evaluation of the first cycle of the team's Exploitability Index. "Four of the issues that we said where consistent exploit code was likely did have exploit code appear over the first two weeks. And another key was that in no case did we rate something too low."

The index, launched last month, rates each vulnerability using a three-step system. It predicts, in descending order of severity, the probability that researchers or hackers would come up with a consistently working exploit or develop an exploit that works only some of the time, or whether they would fail to craft attack code at all.

The predictions are valid for the following 30 days, or until the next cycle of patches is released.

Of the nine October vulnerabilities marked "Consistent exploit code likely," four did, in fact, end up with exploit code available, said Reavey, for an accuracy rate of 44%. None of the nine tagged "Inconsistent exploit code likely" had seen actual attack code. But Microsoft correctly called the four bugs last month tagged with "Functioning exploit code unlikely." As Reavey said, exploit code did not appear for any of the four.

All told, Microsoft correctly predicted eight out of October's 20 vulnerabilities' exploitability, an accuracy rate of 40%. (One of the month's 21 bugs did not receive a rating, as Microsoft said public exploit code was already circulating, making a label moot.)

That accuracy rate was down slightly from what Microsoft claimed during a five-month internal run of the index before it announced the program in August at the Black Hat security conference. According to a presentation Reavey gave at the conference, during the five months it assigned ratings, Microsoft correctly predicted the exploit code availability of 17 out of 36 bugs, for an accuracy rate of 47%.

October's showing didn't faze Reavey, who said what is key is that Microsoft nailed the four for which exploit code was unlikely. "It's important that we don't rate something less likely [to have exploit code] than it turns out to be," he said, "because then customers would have inaccurate information for prioritizing patches."

Microsoft has promoted the index as another piece of information that users, particularly enterprises, can use to decide which vulnerabilities should be patched immediately and which ones can wait.

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