Unbound before 1.10.1 has Insufficient Control of Network Message Volume, aka an "NXNSAttack" issue. This is triggered by random subdomains in the NSDNAME in NS records.
Unbound before 1.9.4 accesses uninitialized memory, which allows remote attackers to trigger a crash via a crafted NOTIFY query. The source IP address of the query must match an access-control rule.
A flaw was found in the way unbound before 1.6.8 validated wildcard-synthesized NSEC records. An improperly validated wildcard NSEC record could be used to prove the non-existence (NXDOMAIN answer) of an existing wildcard record, or trick unbound into accepting a NODATA proof.
iterator.c in NLnet Labs Unbound before 1.5.1 does not limit delegation chaining, which allows remote attackers to cause a denial of service (memory and CPU consumption) via a large or infinite number of referrals.