What is the new Church teaching regarding masturbation?
There is actually no new teaching on masturbation.
The Church has always definitively taught that masturbation is “an intrinsically and gravely disordered action
“By masturbation is to be understood the deliberate stimulation of the genital organs in order to derive sexual pleasure. “Both the Magisterium of the Church, in the course of a constant tradition, and the moral sense of the faithful have been in no doubt and have firmly maintained that masturbation is an intrinsically and gravely disordered action.”138 “The deliberate use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose.” For here sexual pleasure is sought outside of “the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved.” – CCC 2352
It is part of the sixth commandment, and (CCC 1859), and it is a mortal sin when committed with full knowledge and consent. (CCC 1854-64).