---
id: CVE-2026-100666
title: >-
  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 resp…
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 resp…
severity: high
cvss: 7.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L'
cwe:
  - CWE-444
vendor: netty
product: netty
affected:
  - netty >= 4.2.0.Final < 4.2.17.Final
  - netty < 4.1.137.Final
published: '2026-09-26'
updated: '2026-09-26'
sourceUpdated: '2026-09-26T14:16:49.830'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100666'
references:
  - url: 'https://github.com/netty/netty/security/advisories/GHSA-2g6j-r8q9-5hr8'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/netty-4.2.0-through-4.2.17-response-desynchronization-via-httpservercodec
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-26T13:33:20.915Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.