53 Pa. Stat. § 7438
All sheriffs' sales of real estate for the non-payment of taxes, sewer liens, pavement liens and other municipal liens, heretofore held under the provisions of any act of Assembly, where the liens for such taxes and other municipal claims were filed and where the taxes assessed or other municipal claims were actually due and unpaid, are hereby made valid, notwithstanding the fact that prior to such sales executions upon any judgments recovered upon any such taxes and other municipal claims have been by writ of fieri facias instead of by writ of levari facias, and the titles to all such real estate in the hands of the purchasers thereof, their heirs, grantees and assigns are hereby declared to be good and valid to all intents and purposes.
The provisions of this act shall not apply in any instance where the validity of any such sale or the title to the premises purchased thereat has been made the subject of litigation in any court of the Commonwealth prior to the approval of this act.
53 P.S. § 7438