Here we go again, another exploit has been found in BIND, this time it has to do with dodgy dynamic updates. If you send it a specific update you can cause the name server to exit (i.e. crash!). Basically, if your DNS goes down then so does most of your network, so this is a pretty serious DoS exploit.
You should patch all your name servers. It affects any servers that are master for 1 or more zones, but as a properly configured name server, regardless of role, should be master for the loopback zone, 0.0.127.in-addr.arpa, then effectively ALL your name servers are master for at least 1 zone and are vulnerable. So just be done with it and patch them all.
ISC have already released an update which the various vendors (e.g. Infoblox and VitalQIP) are rolling into their code.
More info here: