Proposal for CVSS future embrace

["Mr. Stefan Hagen" <stefan@hagen.link>]

Dear members,

to facilitate the business of our TC, I did many simple transformations on the contributed content from v1.1 and the XSD kindly provided by Feng Cao which seeded the v1.2 drafts until now.

This night I did a first real modelling that would IMO better represent the transitive task of embedding and relating CVSS information of various versions. 

I hereby suggest to replace in vuln.xsd the hard wired V2/V3 mimic with the following:

A) Type for the vector (cvssVector):

Only one type (which constrains the length to the maximum needed for v2 and v3) and hopefully the future versions.

        String representing the components needed to compute the
        various scores for CVSS versions 2 and 3. Note, that v3 scores can be longer than v2 scores
        (up to 138 characters). It is assumed, that future versions of CVSS maintain the structure
        of the information break down and the required vector length.


B) Only a ScoreSet *but* with a required Version attribute (xs:positiveInteger)

      This will hold the CVSS version that the content  conforms to. 
      Versions 2 and 3 fit the structure. It is assumed, that future versions 4, 5, ... will also fit.

C) The Container content of every [0, nifty] ScoreSet to be a sequence:

     BaseScore (cvssv3:zeroToTenDecimalType) [1, 1]
     TemporalScore (cvssv3:zeroToTenDecimalType) [0, 1]
     EnvironmentalScore (cvssv3:zeroToTenDecimalType) [0, 1]
     Vector (vuln:cvssVector) [0, 1]
     vuln:ProductID [0, infty]

    I suggest we use the cvssv3:zeroToTenDecimalType or to be more concise declare
    our own finite field for these 0.0, 0.1, ... 10.0 allowed values.

D) Change the path value of the selector in the uniqueness constraint UniqueScoreSetProductID into:

    .//vuln:CVSSScoreSets/vuln:ScoreSet/vuln:ProductID    


All in all this embraces the future in a reasonable way, and should allow for easy migration of older documents.

Please note, that currently the per CVSSv3 required fixed prefix for vectors is not always 
used "in the wild" (and understandably so, as our cvrf v1.1 length might forbid legitimate values in CVSS v3.
So a Version attribute on a single ScoreSet element instance might be an enhancement for existing documents
when being transformed (see the Oracle example, where the CVSS3.0 prefix would now be signalled
via the Version attribute value "3".

Any feedback greatly appreciated esp. practical problems not known to me in my tower of thought ;-)


Details:

A)

  <xs:simpleType name="cvssVector">
    <xs:annotation>
      <xs:documentation xml:lang="en">String representing the components needed to compute the
        various scores for CVSS versions 2 and 3. Note, that v3 scores can be longer than v2 scores
        (up to 138 characters). It is assumed, that future versions of CVSS maintain the structure
        of the information break down and the required vector length.</xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:token">
      <xs:maxLength value="140"/>
    </xs:restriction>
  </xs:simpleType>

B) and C)

              <xs:element name="ScoreSet" minOccurs="0" maxOccurs="unbounded">
                <xs:annotation>
                  <xs:documentation xml:lang="en">CVSS scores for a given product ID. If the
                    ProductID attribute is omitted, the score applies to all vulnerable
                    products.</xs:documentation>
                </xs:annotation>
                <xs:complexType>
                  <xs:sequence>
                    <xs:element name="BaseScore" type="cvssv3:zeroToTenDecimalType" minOccurs="1"
                      maxOccurs="1">
                      <xs:annotation>
                        <xs:documentation xml:lang="en">The CVSS Base Score is the numeric value of
                          the computed CVSS Base Score which should be a float from 0 –
                          10.0.</xs:documentation>
                      </xs:annotation>
                    </xs:element>
                    <xs:element name="TemporalScore" type="cvssv3:zeroToTenDecimalType"
                      minOccurs="0" maxOccurs="1">
                      <xs:annotation>
                        <xs:documentation xml:lang="en">The CVSS Base Score is the numeric value of
                          the computed CVSS Temporal Score which should be a float from 0 –
                          10.0.</xs:documentation>
                      </xs:annotation>
                    </xs:element>
                    <xs:element name="EnvironmentalScore" type="cvssv3:zeroToTenDecimalType"
                      minOccurs="0" maxOccurs="1">
                      <xs:annotation>
                        <xs:documentation xml:lang="en">The CVSS Base Score is the numeric value of
                          the computed CVSS Environmental Score which should be a float from 0 –
                          10.0.</xs:documentation>
                      </xs:annotation>
                    </xs:element>
                    <xs:element name="Vector" type="vuln:cvssVector" minOccurs="0" maxOccurs="1">
                      <xs:annotation>
                        <xs:documentation xml:lang="en">The CVSS Vector string is the official
                          notation that contains all of the values used to compute the Base,
                          Temporal, and Environmental scores.</xs:documentation>
                      </xs:annotation>
                    </xs:element>
                    <xs:element ref="vuln:ProductID" minOccurs="0" maxOccurs="unbounded"/>
                  </xs:sequence>
                  <xs:attribute name="Version" type="xs:positiveInteger" use="required">
                    <xs:annotation>
                      <xs:documentation xml:lang="en">The CVSS version that the content
                        conforms to. Versions 2 and 3 fit the structure. It is assumed, that
                        future versions 4, 5, ... will also fit.</xs:documentation>
                    </xs:annotation>
                  </xs:attribute>
                </xs:complexType>

D)

    <xs:unique name="UniqueScoreSetProductID">
      <xs:annotation>
        <xs:documentation xml:lang="en">This is to ensure that each CVSS score set mentions a given
          ProductID only one.</xs:documentation>
      </xs:annotation>
      <xs:selector xpath=".//vuln:CVSSScoreSets/vuln:ScoreSet/vuln:ProductID"/>
      <xs:field xpath="."/>
    </xs:unique>




All the best,
Stefan.