$|V_{ub}|$ from exclusive $B$ and $D$ decays

We propose a model-independent method to determine the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ from exclusive $B$ and $D$ decays. Combining information obtainable from $B\to \rho\ell\bar\nu_\ell$, $B\to K^*\nu\bar\nu$, $D\to \rho\bar\ell\nu_\ell$ and $D\to K^*\bar\ell\nu_\ell$, a determination of $|V_{ub}|$ is possible, with an uncertainty from theory of around 10\%. Theoretical uncertainties in the $B\to K^*\ell\bar\ell$ decay rate are discussed.