Add support for CVSSv4

[jobiewinserapck]

-Added class CVSS4 -Based the CVSS4 class on the js implementation found here: https://github.com/RedHatProductSecurity/cvss-v4-calculator -Added new tests for CVSS4 -Added new constants and exceptions for CVSS4 -Added json schema for CVSS4

[skontar]

This looks really good. Thank you!

[skontar]

@mprpic can you please check CI? It seems to fail for some reason.

[skontar]

@jobiewinserapck I presume you used the js implementation to generate test vectors?

[jobiewinserapck]

Yes, I generated the vectors using the js implementation. I could Maybe get some screenshots tomorrow of how I did so. If thats helpful.

The only test failures I encountered after writing this was due to python3's rounding not being "away from zero", causing scores such as 7.25 to round towards 7.2 rather than 7.3 as expected (hence the round_away_from_zero func)

[skontar]

No need for screenshots, just curious. Rounding was always "fun" previously. I am glad you resolved it easily.

[skontar]

@jobiewinserapck can you rebase with master? I think that should re-run the CI with latest setup.

[jobiewinserapck]

Sure thing I'll do that ASAP tomorrow morning

[skontar]

@mprpic can you please review?

[jobiewinserapck]

I'ved added those improvements, thanks for that @skontar!

[marco-silva0000]

just commenting for support, gogogo

[jobiewinserapck]

Just commenting to say I've reformatted cvss/cvss4.py, hopefully the pipeline will pass on next run

[jobiewinserapck]

I've pushed up a commit addressing the issues raised by @mprpic.

I also added some additional tests for malformed cvss strings

[skontar]

@mprpic please re-review.

[skontar]

@jobiewinserapck there were recent changes to rounding in official Javascript implementation. Would you be so kind and double-check everything is still shiny and both implementations match? I think that the Python one will be more correct as it uses Decimal.

[AdrianVollmer]

I don't think round_away_from_zero is correct:

$ python << EOF
from decimal import ROUND_HALF_UP
from decimal import Decimal as D
def round_away_from_zero(x, dp=1):
    return float(D(x).quantize(D("0." + "0" * dp), rounding=ROUND_HALF_UP))

for i in range(6):
    print(round_away_from_zero(i + 0.05))
EOF
0.1
1.1
2.0
3.0
4.0
5.0

It's inconsistent.

I would have said we should just do round(x*10)/10 like the JavaScript implementation, but Math.round(0.5) is 1 in JS and round(0.5) is 0 in Python3 and 1 in Python2. Python3 follows IEEE 754.

The specification document is not clear on which rounding convention should be used:

This score is rounded to one decimal place.

[skontar]

Correct .quantize call should be able to resolve that difference. I do not recall what we did for v3.1 but we were able to get exactly the same results between Python and Javascript.

[skontar]

@AdrianVollmer if the input is Decimal then round_away_from_zero works correctly I think.

>>> float((D(2) + D(5) / D(100)).quantize(D("0.0"), rounding=ROUND_HALF_UP))
2.1

[AdrianVollmer]

Okay, but this function is only used once here and is passed a float:

https://github.com/RedHatProductSecurity/cvss/blob/c5dd7e2f0bcda1b32d509cce59a6db7c94bbec64/cvss/cvss4.py#L558

[AdrianVollmer]

I think this function will suit this particular use case:

def round_away_from_zero(value):
    # Only works correctly for positive values
    return int(value * 10 + 0.5) / 10.0

Since we only need to round values between 0.0 and 10.0, it should be fine.

$ python << EOF
for i in range(10):
 print(int((i+0.05)*10 + 0.5)/10)
EOF
0.1
1.1
2.1
3.1
4.1
5.1
6.1
7.1
8.1
9.1