First it is the Oath against Modernism, also known as the Anti-Modernist oath. While it is no longer required as it once was as a condition of ordination to Major Orders, the principles still remain.
There are some who are caught in the world of conspiracies who claim that the removal of the requirement to take the oath was a plot to endorse Modernism.
I took the oath. I still hold to the oath. There are however groups of laymen who have no formal formation or formal Theological training who have spread the disinformation based on their limited views of the Church that Modernism is endorsed by the Pope and the Curia.
While there are Modernists in the clergy, and where prior to Vatican II (the oath did not remove them from the Church prior to the Council, it just made them go underground.) there is an oath which instructors in Catholic Colleges and Universities are required to take which promises to teach only what the Church teaches. The recent crackdown on the Women Religious who advocate amoral lifestyles should show that the Vatican takes the subject seriously.