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Medium

Netty 4.2.0 through 4.2.16 Response Desynchronization via HttpServerCodec

Type: advisorySources: OSV

Netty's HttpServerCodec (io.netty:netty-codec-http) in versions 4.2.0.Final through 4.2.16.Final and in versions up to and including 4.1.136.Final pairs each outbound response with an inbound request by calling pollMethod() once per response, including for 1xx informational responses. If a client pipelines an HTTP/1.1 GET carrying an Expect: 100-continue header followed by a HEAD request, the 100 Continue response consumes the queued GET method, so the subsequent 200 OK for the GET is paired with HEAD and its body is dropped, while the following 200 OK for the HEAD request is written with a body. This desynchronizes HTTP parsing on the connection: the GET entity is never delivered and the HEAD response body is interpreted as the GET body, resulting in response splitting and unsafe connection reuse. Fixed in 4.2.17.Final and 4.1.137.Final.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-100666
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 04:14 UTC · Revision 1

Source evidence

Netty 4.2.0 through 4.2.16 Response Desynchronization via HttpServerCodec

core-osv · Original source

Published 26 Sept 2026, 13:23 UTC

Netty's HttpServerCodec (io.netty:netty-codec-http) in versions 4.2.0.Final through 4.2.16.Final and in versions up to and including 4.1.136.Final pairs each outbound response with an inbound request by calling pollMethod() once per response, including for 1xx informational responses. If a client pipelines an HTTP/1.1 GET carrying an Expect: 100-continue header followed by a HEAD request, the 100 Continue response consumes the queued GET method, so the subsequent 200 OK for the GET is paired with HEAD and its body is dropped, while the following 200 OK for the HEAD request is written with a body. This desynchronizes HTTP parsing on the connection: the GET entity is never delivered and the HEAD response body is interpreted as the GET body, resulting in response splitting and unsafe connection reuse. Fixed in 4.2.17.Final and 4.1.137.Final.

osv:CVE-2026-100666
Complete source record
{
  "id": "f430ebf669603f7bbbb496adee6d82814c2f7498d0eba08ac534641392110745",
  "url": "https://osv.dev/vulnerability/CVE-2026-100666",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Netty 4.2.0 through 4.2.16 Response Desynchronization via HttpServerCodec",
    "summary": "Netty's HttpServerCodec (io.netty:netty-codec-http) in versions 4.2.0.Final through 4.2.16.Final and in versions up to and including 4.1.136.Final pairs each outbound response with an inbound request by calling pollMethod() once per response, including for 1xx informational responses. If a client pipelines an HTTP/1.1 GET carrying an Expect: 100-continue header followed by a HEAD request, the 100 Continue response consumes the queued GET method, so the subsequent 200 OK for the GET is paired with HEAD and its body is dropped, while the following 200 OK for the HEAD request is written with a body. This desynchronizes HTTP parsing on the connection: the GET entity is never delivered and the HEAD response body is interpreted as the GET body, resulting in response splitting and unsafe connection reuse. Fixed in 4.2.17.Final and 4.1.137.Final.",
    "evidence": "osv:CVE-2026-100666",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-100666",
      "aliases": [
        "CVE-2026-100666",
        "GHSA-2g6j-r8q9-5hr8"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/netty/netty",
              "type": "GIT",
              "events": [
                {
                  "introduced": "09e64d259c99be8b5b2a471a78f11e65eb82598a"
                },
                {
                  "fixed": "e0789d32c72f46fd2e7c99b6fdbbf7e2f4409e44"
                },
                {
                  "introduced": "0"
                },
                {
                  "fixed": "5471f0a6ffa4ab39db22c468c6c851af4ecae709"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "4.2.0.Final"
                      },
                      {
                        "fixed": "4.2.17.Final"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "4.1.137.Final"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  }
                ]
              }
            }
          ],
          "versions": [
            "netty-4.1.136.Final",
            "netty-4.2.16.Final",
            "netty-4.1.135.Final",
            "netty-4.2.15.Final",
            "netty-4.1.134.Final",
            "netty-4.2.14.Final",
            "netty-4.1.133.Final",
            "netty-4.2.13.Final",
            "netty-4.2.12.Final",
            "netty-4.1.132.Final",
            "netty-4.2.11.Final",
            "netty-4.1.131.Final",
            "netty-4.2.10.Final",
            "netty-4.2.9.Final",
            "netty-4.1.130.Final",
            "netty-4.2.8.Final",
            "netty-4.1.129.Final",
            "netty-4.1.128.Final",
            "netty-4.2.7.Final",
            "netty-4.2.6.Final",
            "netty-4.1.127.Final",
            "netty-4.2.5.Final",
            "netty-4.1.126.Final",
            "netty-4.1.125.Final",
            "netty-4.2.4.Final",
            "netty-4.1.124.Final",
            "netty-4.1.123.Final",
            "netty-4.2.3.Final",
            "netty-4.2.2.Final",
            "netty-4.1.122.Final",
            "netty-4.2.1.Final",
            "netty-4.1.121.Final",
            "netty-4.1.120.Final",
            "netty-4.2.0.Final",
            "netty-4.1.119.Final",
            "netty-4.1.118.Final",
            "netty-4.1.117.Final",
            "netty-4.1.116.Final",
            "netty-4.1.115.Final",
            "netty-4.1.114.Final",
            "netty-4.1.113.Final",
            "netty-4.1.112.Final",
            "netty-4.1.111.Final",
            "netty-4.1.110.Final",
            "netty-4.1.109.Final",
            "netty-4.1.108.Final",
            "netty-4.1.107.Final",
            "netty-4.1.106.Final",
            "netty-4.1.105.Final",
            "netty-4.1.104.Final",
            "netty-4.1.103.Final",
            "netty-4.1.102.Final",
            "netty-4.1.101.Final",
            "netty-4.1.100.Final",
            "netty-4.1.99.Final",
            "netty-4.1.98.Final",
            "netty-4.1.97.Final",
            "netty-4.1.96.Final",
            "netty-4.1.95.Final",
            "netty-4.1.94.Final",
            "netty-4.1.93.Final",
            "netty-4.1.92.Final",
            "netty-4.1.91.Final",
            "netty-4.1.90.Final",
            "netty-4.1.89.Final",
            "netty-4.1.88.Final",
            "netty-4.1.87.Final",
            "netty-4.1.86.Final",
            "netty-4.1.85.Final",
            "netty-4.1.84.Final",
            "netty-4.1.83.Final",
            "netty-4.1.82.Final",
            "netty-4.1.81.Final",
            "netty-4.1.80.Final",
            "netty-4.1.79.Final",
            "netty-4.1.78.Final",
            "netty-4.1.77.Final",
            "netty-4.1.76.Final",
            "netty-4.1.75.Final",
            "netty-4.1.74.Final",
            "netty-4.1.73.Final",
            "netty-4.1.72.Final",
            "netty-4.1.71.Final",
            "netty-4.1.70.Final",
            "netty-4.1.69.Final",
            "netty-4.1.68.Final",
            "netty-4.1.67.Final",
            "netty-4.1.66.Final",
            "netty-4.1.65.Final",
            "netty-4.1.64.Final",
            "netty-4.1.63.Final",
            "netty-4.1.62.Final",
            "netty-4.1.61.Final",
            "netty-4.1.60.Final",
            "netty-4.1.59.Final",
            "netty-4.1.58.Final",
            "netty-4.1.57.Final",
            "netty-4.1.56.Final",
            "netty-4.1.55.Final",
            "netty-4.1.54.Final",
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            "netty-4.1.51.Final",
            "netty-4.1.50.Final",
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            "netty-4.1.48.Final",
            "netty-4.1.47.Final",
            "netty-4.1.46.Final",
            "netty-4.1.45.Final",
            "netty-4.1.44.Final",
            "netty-4.1.43.Final",
            "netty-4.1.42.Final",
            "netty-4.1.41.Final",
            "netty-4.1.40.Final",
            "netty-4.1.39.Final",
            "netty-4.1.38.Final",
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            "netty-4.1.27.Final",
            "netty-4.1.26.Final",
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            "netty-4.1.0.CR1",
            "netty-4.1.0.Beta8",
            "netty-4.1.0.Beta7",
            "netty-4.1.0.Beta6",
            "netty-4.1.0.Beta5",
            "netty-4.1.0.Beta4",
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            "netty-4.0.0.Alpha6",
            "netty-4.0.0.Alpha5",
            "netty-4.0.0.Alpha4",
            "netty-4.0.0.Alpha3",
            "netty-4.0.0.Alpha2",
            "netty-4.0.0.Alpha1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-100666.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:26.075205634Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/100xxx/CVE-2026-100666.json",
        "https://github.com/netty/netty/security/advisories/GHSA-2g6j-r8q9-5hr8",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-100666",
        "https://www.vulncheck.com/advisories/netty-4.2.0-through-4.2.17-response-desynchronization-via-httpservercodec"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-444"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/100xxx/CVE-2026-100666.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-100666",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 492412,
  "published_at": "2026-09-26T13:23:31.961+00:00"
}