Showing a CBC-MAC is not preimage resistant with a proof
According to wikipedia's page on CBC-MAC:

If the block cipher used is secure (meaning that it is a pseudorandom permutation), then CBC-MAC is secure for fixed-length messages.[1] However, by itself, it is not secure for variable-length messages. Thus, any single key must only be used for messages of a fixed and known length.

Your case presents no such vulnerability, since you're hashing a fixed number of blocks ($1$, to be exact). If you were to compute the CBC-MAC of a variable-length message you could perform such a preimage attack.