bind: denial of service

An error in the parsing of incoming responses allows some records with
an incorrect class to be accepted by BIND instead of being rejected as
malformed. This can trigger a REQUIRE assertion failure when those
records are subsequently cached. Intentional exploitation of this
condition is possible and could be used as a denial-of-service vector
against servers performing recursive queries.

An attacker who can cause a server to request a record with a malformed
class attribute can use this bug to trigger a REQUIRE assertion in db.c,
causing named to exit and denying service to clients. The risk to
recursive servers is high. Authoritative servers are at limited risk if
they perform authentication when making recursive queries to resolve
addresses for servers listed in NS RRSETs.