Security experts evaluate updated scoring system

CVSS v2 helps IT managers prioritise threats

A standardized and vendor-neutral system that measures IT vulnerabilities has been updated to help IT managers prioritize their response to security potential threats.

The second version of the Common Vulnerability Scoring System, or CVSS v2, calculates a threat score based on a series of measurements referred to as metrics, making it the IT equivalent of the U.S. Homeland Security Advisory System, but without the color-coded chart. The system measures three areas of concern: 1) base metrics which captures the characteristics of a vulnerability that are constant with time and across user environments.; 2) temporal metrics for characteristics that evolve over the lifetime of vulnerability; and 3) environmental metrics for characteristics of a vulnerability that are associated with a user's IT environment.

Gavin Reid, chair of the CVSS-Special Interest Group, said because CVSS v1 didn't go through a rigorous peer review stage, problems with the formula led to some inaccurate scoring.

"We've increased the fidelity and the accuracy of the equations by really spending a lot of time working on the formula," Reid said. "CVSS v1 had a couple of areas where a bunch of the vulnerabilities sort of clumped on certain scores like seven or 10 and all the vulnerabilities seemed to get those scores. So, we tried to ensure that we used the full available spectrum from zero to 10, but in doing that, we still wanted to increase the fidelity and not make things worse." To achieve a more accurate formula, Reid said the updated system was tested by members of CVSS-SIG, comprised of various IT professionals, for two years on their experiences with real-world vulnerabilities.

"If there was a vulnerability that we all agreed should have scored higher we'd look to see the reasons why and make the changes to the system," Reid said. "We also added an extra layer of granularity to areas that were too binary." Robert Beggs, CEO of Toronto-based security consultancy Digital Defence, said the newest update is an incredible step up from the first one and ranks CVSS as the best publicly available vulnerability scoring systems.

But Beggs warned that IT managers using systems like these can quickly run into an affliction called "managing by the numbers."

"The numbers hide some very important things," Beggs said. "The problem is not everyone configures the target system the same way, because if everyone configured them securely there would be no vulnerabilities. The issue we're facing is it just takes one misconfiguration and then something that has a relatively low vulnerability score can take over your network."

Beggs referenced the 2001 outbreak of the Code Red worm as an example of a vulnerability that would probably be rated low on the CVSS system but ended up finding weakened servers and doing significant damage.

"The patch was out for six to eight months before it ever attacked," Beggs said. "The reason large organizations fell victim to Code Red wasn't that they hadn't applied the patch, it was they had some yahoo in tech support that set up their own server to see how it work or some developer who set up his own server didn't patch use the patches."

Beggs said the system also may bring added complexity to IT managers who are handcuffed by competing priorities. "I could give you a 9.7 level vulnerability which means, 'fix it right now,'" Beggs said. "But the manager might say, 'it's a production server and we can't bring it down, so we're going to have to accept the risks because it's generating revenue for our business.'"

Tyler Reguly, security research engineer at nCircle Network Security, disagreed, saying that the CVSS is far more useful to him than any other system, including Microsoft's vulnerability system used on Patch Tuesday. He said prove of this is in the fact that a lot more vendors such as Cisco and Oracle are now releasing CVSS scores with their patches.

"Microsoft's gone through a few of them and they've seemed to have settled on this critical, important, and moderate model," Reguly said. "The CVSS far exceeds that system and I don't think there is anything close to touching it right now. It's got a lot of support, a lot of backing, and with version two it's getting much more accurate."

Beggs, on the other hand, sees the primary benefit of scoring system for senior managers looking to provide an overview of network security.

"Of those managers and technical staff using this, the real value is going to be at the senior manager level looking at the network as a whole," Beggs said. "It represents the most complete way of generating a scorecard for network security, however, it's success is going to be on how it's going to be used within the organization, meaning management has to avoid the by numbers approach."

And because of this problem, Beggs said that the system may still be more trouble than it's worth and questions what the numeric scores are really adding to network security.

"I've used systems like this before at large organizations," Beggs said. "It always starts off well, but maintaining doing this effectively is a very difficult process. And it really won't happen until we get automated tools that integrate with change control, that integrate with visibility, and that provide strategic way of actually using this information."

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Rafael Ruffolo

ComputerWorld Canada
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