"A race condition could trigger an assertion failure when a large number of incoming packets were being rejected. This flaw is disclosed in CVE-2019-6471."
https://downloads.isc.org/isc/bind9/9.14.4/RELEASE-NOTES-bind-9.14.4.html
https://downloads.isc.org/isc/bind9/9.14.4/RELEASE-NOTES-bind-9.14.4.html