AES-CBC Padding Explained
Encrypting plaintext using Advanced Encryption Standard (AES) in Cipher Block Chaining (CBC) mode requires the plaintext to be a multiple of 16 bytes long. All plaintext is padded before encryption. The padding method is described in Section 6.3 of PKCS #7.
The Padding Technique If the last block of the plaintext message has 1 byte (e.g., if the plaintext is 17, 33, or 49 bytes), then 15 bytes of the value 0x0f (15) are added to the end of the plaintext.