CVE-2018-5738

Change #4777 (introduced in October 2017) introduced an unforeseen issue in
releases which were issued after that date, affecting which clients are
permitted to make recursive queries to a BIND nameserver. The intended (and
documented) behavior is that if an operator has not specified a value for
the “allow-recursion” setting, it SHOULD default to one of the following:
none, if “recursion no;” is set in named.conf; a value inherited from the
“allow-query-cache” or “allow-query” settings IF “recursion yes;” (the
default for that setting) AND match lists are explicitly set for
“allow-query-cache” or “allow-query” (see the BIND9 Administrative
Reference Manual section 6.2 for more details); or the intended default of
“allow-recursion {localhost; localnets;};” if “recursion yes;” is in effect
and no values are explicitly set for “allow-query-cache” or “allow-query”.
However, because of the regression introduced by change #4777, it is
possible when “recursion yes;” is in effect and no match list values are
provided for “allow-query-cache” or “allow-query” for the setting of
“allow-recursion” to inherit a setting of all hosts from the “allow-query”
setting default, improperly permitting recursion to all clients. Affects
BIND 9.9.12, 9.10.7, 9.11.3, 9.12.0->9.12.1-P2, the development release
9.13.0, and also releases 9.9.12-S1, 9.10.7-S1, 9.11.3-S1, and 9.11.3-S2
from BIND 9 Supported Preview Edition.