When binding against a DN during authentication, the reply from 389-ds-base will be different whether the DN exists or not. This can be used by an unauthenticated attacker to check the existence of an entry in the LDAP database.
https://github.com/389ds/389-ds-base/issues/4480
https://github.com/389ds/389-ds-base/commit/cc0f69283abc082488824702dae485b8eae938bc
https://github.com/389ds/389-ds-base/commit/b6aae4d8e7c8a6ddd21646f94fef1bf7f22c3f32