Kornfeld was involved in numerous controversies. In 1993 a lawsuit opposed him and David P. Tunick, a Manhattan dealer concerning the authenticity of a signature. In 2017, it was discovered that the son of
Adolf Hitler's art dealer
Hildebrand Gurlitt had been selling artworks from his secret stash in Munich through Kornfeld in Switzerland. Kornfeld denied selling Nazi looted art. In 2018, the heirs to other Jewish collectors who had been looted, August et
Serena Lederer, got a court order to compel Kornfeld to supply information about a Schiele painting they had owned. In 2019 a judge ordered that two
Schieles that Kornfeld had sold be restituted to the heirs of a
Holocaust victim
Fritz Grünbaum because they had been looted by
Nazis. In September 2023 the Manhattan DA seized several Schiele paintings that Kornfeld had sold to Otto Kallir's NYC-based
Galerie St. Etienne, "with no provenance whatsoever". After an investigation by Assistant District Attorney
Matthew Bogdanos, Chief of the Antiquities Trafficking Unit, Assistant District Attorney Edward Smith, Investigative Analyst Hilary Chassé, and Special Agents Megan Buckley and Robert Mancene of
Homeland Security Investigations, "all seven drawings were seized and voluntarily surrendered by the holding institutions and estates after they were presented with evidence that they were stolen by the Nazis. The
Art Institute of Chicago refused, citing Kornfeld's story that he had purchased the Schiele known as
The Russian Prisoner legally and denying evidence that Kornfeld had forged the signature of Mathilde Lukacs on a document. In February 2024, the Manhattan DA filed a 160 page motion accusing the Art Institute of Chicago of "willful blindess" and detailing the evidence that Kornfeld had falsified the provenance in order to conceal the sale of art looted from the Jewish Holocaust victim
Fritz Grünbuaum. == Philanthropy ==