Update to version 9.6.1-P1 which addresses a remote DoS vulnerability:
Receipt of a specially-crafted dynamic update message may
cause BIND 9 servers to exit. This vulnerability affects all
servers -- it is not limited to those that are configured to
allow dynamic updates. Access controls will not provide an
effective workaround.
More details can be found here: https://www.isc.org/node/474
All BIND users are encouraged to update to a patched version ASAP.