---
id: CVE-2026-89044
title: >-
  Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through
  4.2.17.Final fail to properly validate the final transfer coding in the
  Transfer-Encoding header, allowing attackers to smuggle requests by using
  malformed encod…
summary: >-
  Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through
  4.2.17.Final fail to properly validate the final transfer coding in the
  Transfer-Encoding header, allowing attackers to smuggle requests by using
  malformed encod…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-444
vendor: netty
product: netty
affected:
  - 'netty >= 4.1.133, < 4.1.138'
  - 'netty >= 4.2.13, < 4.2.18'
patched:
  - netty 4.2.18
published: '2026-09-10'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T18:17:39.213'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89044'
references:
  - url: 'https://github.com/netty/netty'
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/netty/netty/blob/netty-4.1.137.Final/codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectDecoder.java#L866
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/netty/netty/commit/640d4d3324f7b811a4903d0730c8ccb35500500c
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/netty/netty/commit/ca87393b0e9e13c493d213a268e727a6d44e1585
    label: disclosure@vulncheck.com
  - url: 'https://github.com/netty/netty/releases/tag/netty-4.1.138.Final'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/netty/netty/releases/tag/netty-4.2.18.Final'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/netty/netty/security/advisories/GHSA-hcvj-94mj-jp5c'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/netty-4.1.133-final-through-4.1.137-final-and-4.2.13-final-through-4.2.17-final-http-request-smuggling-via-transfer-encoding
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
epss: 0.00426
epssPercentile: 0.34116
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-18T17:11:17.626681Z'
ingestedAt: '2026-09-12T14:36:59.336Z'
---

## Overview

Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final fail to properly validate the final transfer coding in the Transfer-Encoding header, allowing attackers to smuggle requests by using malformed encoding declarations. Attackers can split Transfer-Encoding headers across multiple lines or use values like 'chunked, xchunked' to bypass validation and decode messages as chunked when the final coding is not chunked, enabling request smuggling attacks.

## Affected

- `netty >= 4.1.133, < 4.1.138`
- `netty >= 4.2.13, < 4.2.18`

## Remediation

Upgrade past the affected range:

- `netty 4.2.18`