Modes like OFB effectively produce a keystream(not unlike a stream cipher) which is then XOR'd with the plaintext to produce the ciphertext.
To decrypt, the same keystream is XOR'd with the ciphertext to produce the plaintext.
If there is no integrity on the ciphertext, you can simply start flipping bits in the ciphertext, and arbitrarily change what the resulting XOR with the keystream will be.
To decrypt, the same keystream is XOR'd with the ciphertext to produce the plaintext.
If there is no integrity on the ciphertext, you can simply start flipping bits in the ciphertext, and arbitrarily change what the resulting XOR with the keystream will be.