Really? Can you even copyright a font? As far as I know, fonts can't be copyrighted, meaning they can be used by anyone without needing a licence. IANAL, but it seems like font users aren't required to comply with attribution and share-alike requirements of the CC licence.
It is vector fonts, which can contain copyrightable code, which can be copyrighted.
With vector fonts containing copyrightable code, are you referring to e.g. TrueType hinting, or OpenType shaping (or very avant-gardely, WASM shaping)? I should hope the glyph-drawing instructions don't fall under this definition of code, because that'd maybe mean SVG `path`s are copyrightable...
What specifics you can get is all described in ML-443.