CVE-2026-86003: CoreDNS DoH/DoQ/gRPC bypass UPDATE rejection enforced on UDP/TCP

CoreDNS accepted RFC 2136 UPDATE messages over DoH, DoH3, DoQ, and DNS-over-gRPC, then allowed the proxy/forward plugin to send them unchanged to an upstream DNS server. UDP, TCP, and DoT rejected the same opcode before plugin dispatch.

If an update-capable upstream trusts CoreDNS’s source address or authenticated connection instead of requiring end-to-end TSIG, an unauthenticated client can use CoreDNS to add, replace, or delete DNS records.