---
id: CVE-2026-100663
title: >-
  Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.2.Final through
  4.2.17.Final does not special-case HTTP/1 CONNECT authority-form
  request-targets when converting HTTP/1 messages to HTTP/3 in
  HttpConversionUtil.toHttp3Headers
summary: >-
  Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.2.Final through
  4.2.17.Final does not special-case HTTP/1 CONNECT authority-form
  request-targets when converting HTTP/1 messages to HTTP/3 in
  HttpConversionUtil.toHttp3Headers. T…
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: '2026-09-26T14:16:49.400'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100663'
references:
  - url: 'https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/netty-http-1-connect-authority-form-mistranslated-to-malformed-http-3
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-26T13:33:20.916Z'
---

## Overview

Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.2.Final through 4.2.17.Final does not special-case HTTP/1 CONNECT authority-form request-targets when converting HTTP/1 messages to HTTP/3 in HttpConversionUtil.toHttp3Headers. The authority-form target (e.g., "CONNECT trusted.example:443") is parsed as a URI, so its host is emitted as :scheme, :path is set to "/", and the HTTP/1 Host header is used as :authority; if no Host header is present the CONNECT target is dropped. In a Netty-based HTTP/1-to-HTTP/3 proxy or gateway, a remote client can send a CONNECT request whose Host header names a different authority than the request-target, producing a malformed HTTP/3 CONNECT whose tunnel :authority is attacker-controlled. This can bypass tunnel allow-lists, egress policy, backend selection, or audit controls that validate the HTTP/1 CONNECT request-target before forwarding over HTTP/3. The issue is fixed in 4.2.18.Final.

## Remediation

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