The Membership For WooCommerce WordPress plugin before 3.1.2 does not check that an API consumer secret has actually been generated before comparing it against the one supplied in a request, allowing unauthenticated attackers to reach its REST routes and disclose any user's membership plan details on sites where the API has been enabled but no keys were ever generated.
https://wpscan.com/vulnerability/957888a4-bb11-42c6-930a-8c836170452b/