New York Consolidated Laws, Real Property Actions and Proceedings Law - RPA § 904. Permissible defendants

1. A tenant by the curtesy or for life or for years, of the entire property, or whoever may be entitled to a contingent or vested remainder or reversion in the entire property, or a person having a lien or interest which attaches to the entire property.  A person specified in this subdivision who is not made a party is not affected by the judgment in the action.

2. A person having a lien on an undivided share or interest in the property.  The nature of the lien and the share or interest to which it attaches shall be specified.

3. An unknown person entitled to an estate or interest in the property sold.  The court shall provide for the protection of his rights, as far as may be, as if he were known and had appeared.

4. The state.