Unbound before 1.4.4 does not send responses for signed zones after mishandling an unspecified query, which allows remote attackers to cause a denial of service (DNSSEC outage) via a crafted query.
http://www.debian.org/security/2011/dsa-2243
http://unbound.nlnetlabs.nl/downloads/unbound-1.4.4.tar.gz
http://packages.debian.org/changelogs/pool/main/u/unbound/unbound_1.4.6-1/changelog