---
id: CVE-2026-100664
title: >-
  Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.2.Final through
  4.2.17.Final builds the HTTP/3 :authority pseudo-header from the HTTP/1 Host
  header before considering the authority of an absolute-form HTTP/1
  request-target…
summary: >-
  Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.2.Final through
  4.2.17.Final builds the HTTP/3 :authority pseudo-header from the HTTP/1 Host
  header before considering the authority of an absolute-form HTTP/1
  request-target…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'
cwe:
  - CWE-20
vendor: netty
product: netty
affected:
  - netty >= 4.2.2.Final < 4.2.18.Final
published: '2026-09-26'
updated: '2026-09-26'
sourceUpdated: '2026-09-26T14:16:49.540'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100664'
references:
  - url: 'https://github.com/netty/netty/security/advisories/GHSA-hfr2-x62w-v49h'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/netty-4.2.2-through-4.2.15-http-1-host-header-authority-confusion
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-26T13:33:20.914Z'
---

## Overview

Netty's HTTP/3 codec (io.netty:netty-codec-http3) versions 4.2.2.Final through 4.2.17.Final builds the HTTP/3 :authority pseudo-header from the HTTP/1 Host header before considering the authority of an absolute-form HTTP/1 request-target. In HttpConversionUtil.toHttp3Headers(HttpMessage, boolean) — reached via Http3FrameToHttpObjectCodec(false) — a non-empty Host header takes precedence over the request-target authority, contrary to the HTTP/1.1 rule that a server receiving an absolute-form request-target must ignore the Host header. In a Netty-based HTTP/1-to-HTTP/3 gateway, proxy, or protocol bridge, a remote client can send a request such as "GET https://trusted.example/admin HTTP/1.1" with "Host: attacker.example", causing components that validate, authorize, or route on the RFC-defined request-target authority to reach a different decision than the upstream HTTP/3 peer, which receives :authority derived from the conflicting Host header. This authority confusion can affect virtual-host routing, allow-list checks, backend selection, cache keys, and URL generation. The advisory reports integrity impact only (no code execution, memory corruption, or availability impact). Fixed in 4.2.18.Final.

## Remediation

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