Unbound before 1.3.4 does not properly verify signatures for NSEC3 records, which allows remote attackers to cause secure delegations to be downgraded via DNS spoofing or other DNS-related attacks in conjunction with crafted delegation responses.
http://secunia.com/advisories/36996
http://secunia.com/advisories/37913
http://unbound.net/pipermail/unbound-users/2009-October/000852.html
http://www.debian.org/security/2009/dsa-1963
http://www.openwall.com/lists/oss-security/2009/10/09/2
http://www.openwall.com/lists/oss-security/2009/10/09/3