The miekg Go DNS package before 1.1.25, as used in CoreDNS before 1.6.6 and other products, improperly generates random numbers because math/rand is used. The TXID becomes predictable, leading to response forgeries.
https://github.com/miekg/dns/pull/1044
https://github.com/miekg/dns/issues/1043
https://github.com/miekg/dns/compare/v1.1.24...v1.1.25