Modification of block cipher in CBC mode I know that CBC is not secure against data modification. Can someone explain to me by illustrating at an example how I could change the last block if I have the encryption of "0"?

Thanks in advance
If you flip bits in cipher text block $E_K(M_i)$ then you flip the same bits in $M_{i+1}$. If you know or guess the value of the last plaintext block then XOR the second to last ciphertext block with the guessed plaintext value. That makes it zero because $v \oplus v = 0$ for all v. It's not so easy to manipulate otherwise.

Edit: I misread encrypted "0" as set plaintext to zero

If $M_i$ is known to be zero then XORing $M_{i-1}$ with $v$ causes block i to decrypt to $v$ instead.