In the spirit of learning about these things, you might want to try these: https://cryptopals.com/
In particular, problem number 17 from set 3 is an attack against CBC mode AES used with Mac-the-Encrypt. Maybe a fun exercise would be to first implement that attack against CBC mode, and then try to see if you can make it work against your CFB-HMAC protocol.
In particular, problem number 17 from set 3 is an attack against CBC mode AES used with Mac-the-Encrypt. Maybe a fun exercise would be to first implement that attack against CBC mode, and then try to see if you can make it work against your CFB-HMAC protocol.