[Dailydave] CVSS is the worst compression algorithm ever

Dave Aitel dave.aitel at cyxtera.com
Tue Jan 8 16:14:00 UTC 2019

I wanted to take a few minutes and do a quick highlight of a paper from CMU-CERT which I think most people have missed out on: https://resources.sei.cmu.edu/asset_files/WhitePaper/2018_019_001_538372.pdf

Towards Improving CVSS - resources.sei.cmu.edu<https://resources.sei.cmu.edu/asset_files/WhitePaper/2018_019_001_538372.pdf>
SOFTWARE ENGINEERING INSTITUTE | CARNEGIE MELLON UNIVERSITY REV-03.18.2016.0 Distribution Statement A: Approved for Public Release; Distribution Is Unlimited TOWARDS IMPROVING CVSS

It's almost as funny a read as their previous best work on how "clientless HTTPS VPNs are insanely dumb<https://www.kb.cert.org/vuls/id/261869/> what were you thinking omg?"

They use a ton of big words in the paper to call CVSS out and give it a shellacking. Like most of you, we have extensive use of CVSS in our consulting practice and I've seen this stuff first hand. CVSS is of course just a buggy compression algorithm for taking complex qualitative data and then putting it on a number line. The paper has three angles here:

  1.  Qualitative mappings into quantitative numbers are a silly thing to do, like people trying to do "social science" by using SurveyMonkey.
  2.  We're pretty sure that the compression algorithm is not, in fact, putting higher risk items as bigger numbers, which is the whole point of the thing.
  3.  Nobody is applying this in any sort of consistent way (which is probably impossible) which is ALSO the whole point of the thing.

It's fine to have a lossy compression algorithm that emphasizes certain aspects of the input signal over others, of course, but an additional CERT/CC critique is we have no reason to think CVSS does this in any useful way.

There's definitely people in the CVSS process (who I will avoid calling out by name) who think ANY quantization is good. But read the paper and decide for yourself - because these are probably serious issues that are turning your entire risk org into a Garbage-In-Garbage-Out org...


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