NSS UBSan builds currently have the following undefined behavior checks enabled by default (set in sanitizers.sh):

bool,signed-integer-overflow,shift,vptr

These are a small subset of all available checks, as well as a partial subset of the default Firefox UBSan build checks:

bool,bounds,enum,function,integer-divide-by-zero,object-size,pointer-overflow,return,vla-bound

The checks have been last updated in NSS 3.29 / 2017 and there has already been a undetected undefined behavior in NSS, which would have been detected with the 'pointer-overflow' check enabled.

=> The same default UBSan checks as in the Firefox builds should probably be enabled.

I spent some time looking at this and I think we can enable the default UBSan checks with a small amount of work. There's two outstanding issues which I've filed child bugs for. Further progress is blocked until fix up the current issues with the CI.

https://hg.mozilla.org/projects/nss/rev/013b4b6ad803f083aa1ad89200e395dcd16fae7d