2 Answers
Generally speaking, exterior primers have a built-in moisture barrier where as interior primers do not… however there is much more in the way they are formulated… which only a paint chemist could explain…
For example Pigmented Shellac Sealer Primer is excellent for interiors and does provide a moisture barrier but does not hold up for exteriors…
Regular Latex interior primers do not provide any moisture barrier … the same is true for some interior oil primers…
It's best to use a product that qualifies as both and is oil based… Kilz makes one like this… along with Zinzer Cover Stain…
At last… read the product labels…