Podlove Podcast Publisher < 3.5.6 - Unauthenticated SQL Injection

The Podlove Podcast Publisher WordPress plugin before 3.5.6 contains a 'Social & Donations' module (not activated by default), which adds the rest route '/services/contributor/(?P<id>[\d]+), takes an 'id' and 'category' parameters as arguments. Both parameters can be used for the SQLi.