Definition
MAC-then-Encrypt
MAC-then-Encrypt is an approach to authenticated encryption in which the MAC is computed over the plaintext, then the plaintext and MAC are encrypted together.
Security
Not Universally Secure
This approach is not secure for all possible combinations of secure ciphers and MACs. It is secure with block ciphers in CBC mode or with stream ciphers, but it was the cause of catastrophic padding-oracle attacks in TLS (POODLE and Lucky 13).