CVE-2026-82399

### Summary CoreDNS parses attacker-controlled DNS section counts before validating them on DNS-over-HTTPS (DoH and DoH3), DNS-over-QUIC (DoQ), and DNS-over-gRPC listeners. An unauthenticated client can use DNS name compression to make one 65,533-byte request allocate more than 10 MiB while it is unpacked. Concurrent requests can exhaust memory and terminate CoreDNS. ### Details The affected request paths call `dns.Msg.Unpack` directly: - [DoH POST and GET decoding](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/plugin/pkg/doh/doh.go#L134-L155). DoH3 uses the same decoder. - [DoQ stream handling](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/core/dnsserver/server_quic.go#L212-L219). - [DNS-over-gRPC query handling](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/core/dnsserver/server_grpc.go#L176-L184). This differs from the [miekg/dns](https://github.com/miekg/dns) UDP and TCP server. Its [`serveDNS`](https://github.com/miekg/dns/blob/v1.1.72/server.go#L628-L643) path decodes the fixed 12-byte header and invokes [`DefaultMsgAcceptFunc`](https://github.com/miekg/dns/blob/v1.1.72/acceptfunc.go#L33-L57) before unpacking the DNS sections. The default policy rejects requests unless `QDCOUNT` is exactly one and also limits the other section counts. CoreDNS's custom transports bypass this early validation. Parsing happens before the plugin chain. Plugin-level rate limiting or request handling cannot prevent the allocation. The fix is to apply `dns.DefaultMsgAcceptFunc` to the fixed header before calling `Msg.Unpack` in each custom request transport. Response decoding must remain separate because the request policy intentionally rejects response headers. ### PoC The PoC runs against the DoH server. Run the following from a clean checkout of CoreDNS v1.14.6. Docker must support container memory limits. The example uses the test certificate already present in the re