Internet Systems Consortium has stated there are a couple vulnerabilities in BIND (DNS server), that can be exploited to cause a DoS.

SIG Query Processing (CVE-2006-4095):
1) An assertion error within the processing of SIG queries can be exploited to crash either a recursive server when more than one SIG(covered) Resource Record set (RRset) is returned or an authoritative server serving a RFC 2535 DNSSEC zone where there are multiple SIG(covered) RRsets.

Excessive Recursive Queries INSIST failure (CVE-2006-4096):
2) An error within the handling of multiple recursive queries can be exploited to trigger an INSIST failure by causing the response to the query to arrive after all clients looking for the response have left the recursion queue.

So ensure you are patched to the current version:  BIND 9.3.3rc2, BIND 9.3.2-P1, BIND 9.2.7rc1, or BIND 9.2.6-P1.

Updates are available here.

As of this time we have not received any information on an exploit for either vulnerability.