Per the commentary in my RSC-2CE (Ignatius - Scott Hahn):
The Eastern Church accepted Paul as the author, whereas the Western Church didn’t initially accept - and some explicitly denied it. In the 4th century, the Western Church shifted towards accepting Paul.
In the 16th Century, the question came up again. As posted by another, Trent (4th session) defined it as a letter of Paul, but the statement ‘does not amount to a dogmatically binding attribution’.
One point -if you look at the beginning of Hebrews, it does not start out with a greeting from Paul.
The final words from the Commentary suggest that it was written by a Pauline disciple. "Thus, the tradition of Pauline authorship remains reasonable if we take it to mean that Hebrews’ doctrinal content is Paul’s, even if its literary composition is the work of an unknown collaborator who expressed Paul’s teachings in a particularly elegant way’.
Count me among those saying that this is nothing that should be discussed during Mass. Authorship of the various books of the Bible can be a very controversial subject.