What is the status of a pan used to bake bread that is halachically forbidden as dairy or meat bread?
According to most poskim to pan is milchig, but it is not issur, and it doesn’t have to kashered. The reason is as follows. The poskim discuss what is the halacha if the milchig bread got mixed with other breads, do we saythe the bread is considered inherently assur, and therefore it would need bitul, or do we say that it is merely an enactment not to actually eat he bread, but not that the bread is inherently assur, and therefore it wouldn’t need bitul. According to the poskim that say that milchig bread is not inherently assur, then it surely will not make the pan and the oven trief. That is all regarding the actual bread itself, however if the bread will assur other things, such as a different bread that it touches, is also questionable, and most posim say that it will not assur other foods. According to those poskim that say that it will not assur other foods, the oven would not have to be kashered as if it was trief, however the pan it was baked in will be considered milchig. See sources.
See Pischei Teshuvos Y:D 97-2 and Levushei Srad, Darcei teshuva ibid 5& 11, Shut Tuv Taam Vdaas – Third Edition 180, brought in Daas Torah, Yad Yehuda ( Aruch ibid 4, Aruch Hashulchan ibid 5. Hilchos Basar B’chalav (R’ Z. Hofstadter)14-37&38 that R’ C. Kanievsky, R’ M. Sternbuch, R’ E. Auerbach shlit”a, held that it does assur the utensil that it was baked in. This is also the opinion of other poskim. However R’ M. S. Klien shlit”a holds that it is assur. Also see OU Teshuvos k-329, k-338.