---
title: "CVE-2026-100664: Netty - Broken Access Control"
description: "Netty io.netty:netty-codec-http3 4.2.2.Final through 4.2.17.Final contains an authority confusion vulnerability caused by incorrect precedence of Host header over request-target authority in HTTP/3 :authority pseudo-header construction, letting remote attackers cause inconsistent routing and authorization decisions, exploit requires crafted HTTP/1 requests with conflicting Host headers."
url: https://panop.io/threat-heartbeat/CVE-2026-100664/
---

# CVE-2026-100664 Netty - Broken Access Control

Netty io.netty:netty-codec-http3 4.2.2.Final through 4.2.17.Final contains an authority confusion vulnerability caused by incorrect precedence of Host header over request-target authority in HTTP/3 :authority pseudo-header construction, letting remote attackers cause inconsistent routing and authorization decisions, exploit requires crafted HTTP/1 requests with conflicting Host headers.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.33% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-100664)

## Details

Type

Broken Access Control

Impact

Data Tampering

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Published

26 September 2026

Updated

15 October 2026

Weakness

[CWE-20](https://cwe.mitre.org/data/definitions/20.html)

## Vendor fix

Upgrade to version 4.2.18.Final or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-100664](https://nvd.nist.gov/vuln/detail/CVE-2026-100664)
- [https://github.com/netty/netty/security/advisories/GHSA-hfr2-x62w-v49h](https://github.com/netty/netty/security/advisories/GHSA-hfr2-x62w-v49h)
- [https://www.vulncheck.com/advisories/netty-4.2.2-through-4.2.15-http-1-host-header-authority-confusion](https://www.vulncheck.com/advisories/netty-4.2.2-through-4.2.15-http-1-host-header-authority-confusion)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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