A deficiency in the SRTT (Smoothed Round Trip Time) algorithm in BIND9 was reported that could theoretically allow an attacker to lower the SRTT value that a recursive resolver has associated with an authoritative server.  This could allow the attacker to influence the selection of a specific authoritative server from an NS resource record set with multiple values and thus determine which of multiple authoritative servers for a domain will be queried.

ISC has indicated that they intend to address this deficiency by reimplementing the SRTT algorithm in a future maintenance release of BIND9.  They also note that "the deficiency in the SRTT algorithm is not considered an exploitable security vulnerability on its own".


External References:

https://kb.isc.org/article/AA-01030/169/Operational-Notification-A-Vulnerability-in-the-SRTT-Algorithm-affects-BIND-9-Authoritative-Server-Selection.html