CBC-MAC extension attack, as well as sending two messages (one padded, one unpadded). To leak most of the final block.
```m1 = "SEKAI"c1 = query(m1)
m2 = pad("SEKAI")c2 = query(m2)
m3 = "any message >= 16 bytes"c3 = query(m3)
mForge = m2 || XOR(m3[:16, c1 || c2) || m3[16:]cForge = c3```