WaifUPNP is under: https://www.gnu.org/licenses/lgpl

You may:
distribute the mod(no malware sites)
contribute to the mod
fork/modify the mod
re-upload to curseforge without written consent under a similar name prefixed or suffixed in non forks/ports page as long as credit is given.

You may not:
modify WaifUPNP against the gnu license(make sure source is open when modifying it)