735 ILCS 5/12-149
The right, title and interest of any purchaser acquired at a sale made under or pursuant to any judgment in a proceeding in which the court had jurisdiction of the subject matter and of the parties, and who was not a party to such proceeding, and the right, title and interest of any bona fide assignee or pledgee for value of the certificate of sale under such certificate issued pursuant to a sale based on such judgment rendered in such proceeding who was not a party to such proceeding (whether the purchaser at such sale was a party or not), shall not be affected by any reversal, modification or order setting aside such judgment made in any proceeding to review such judgment, unless at the time of such sale, assignment or pledge, an appeal was pending which operated as a stay of enforcement of the judgment or a petition under Section 2-1401 of this Act had been filed.
735 ILCS 5/12-149