Parse Server before 8.6.93 and 9.0.0 before 9.10.1 does not enforce identity-scoped protectedFields (authenticated, role, or per-user groups) on count queries using the $relatedTo operator, exposing the size of protected Relation fields. An authenticated user who can read the owning object can combine counts with an objectId constraint as a membership oracle to reveal confidential memberships such as private groups or block lists.