21 Pa. Stat. § 288
The title to real estate heretofore sold by any city of the third class of this Commonwealth, if the sale was authorized by an ordinance or resolution of the city council of said city and shall not be attacked in any proceedings instituted within six years after the effective date of this act, or within six years after the date of such sale, whichever date is the earlier, is hereby declared to be good and valid and free and clear of any defects, and any such person, partnership or corporation grantee thereunder, and his or her or its respective heirs, successors and assigns, shall hold and may convey such title and estate, and all such conveyances, heretofore made, are hereby ratified and confirmed. Nothing in this act shall be construed to apply to property which the city acquired other than by purchase.
21 P.S. § 288