We also tend to assume that Paul wrote the epistle to the Hebrews because the theology is deep and the writing style is similar,
Hebrews 2:3 KJV
How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him;
Galatians 1:11-12 KJV
11) But I certify you, brethren, that the gospel which was preached of me is not after man.
12) For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ.
I'm of the opinion that Paul did not write Hebrews.
Much love!