Protestants defend our position in various ways. An excellent one can be seen here, by the late Orthodox Presbyterian Rev. Greg Bahnsen. In response, Catholics ask the question, legitimately, if hypocritically, "Where does the Bible teach sola scriptura?" Again, various answers, some better, some worse, are given. I will offer one that I have not seen from anyone else.
"When they say to you, 'Inquire of the mediums and the necromancers who chirp and mutter,' should not a people inquire of their God? Should they inquire of the dead on behalf of the living? To the teaching and to the testimony! If they will not speak according to this word, it is because they have no dawn" (Isaiah 8:19-20). God, speaking here through the Prophet Isaiah, asks the very question I am addressing: how should the people of God judge truth and falsity? And He gives the only infallible answer: By comparing it to the Word that He had breathed out (II Timothy 3:16), i. e., the Bible.