CVE-2026-89044Public exploitNetwork attack vector

HTTP request smuggling via transfer-coding suffix validation

Published Sep 10, 2026 · Updated Sep 10, 2026

Netty 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final allows remote attackers to smuggle HTTP requests. HttpObjectDecoder.readHeaders treats a raw Transfer-Encoding value ending in chunked as valid instead of parsing and validating the final coding token across all header fields. An exposed HTTP/1 decoder behind a parser-differential intermediary is required, and successful exploitation injects arbitrary HTTP requests.

CVSS severity6.5
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Netty 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final allows remote attackers to smuggle HTTP requests. HttpObjectDecoder.readHeaders treats a raw Transfer-Encoding value ending in chunked as valid instead of parsing and validating the final coding token across all header fields. An exposed HTTP/1 decoder behind a parser-differential intermediary is required, and successful exploitation injects arbitrary HTTP requests.

The record

CVE
CVE-2026-89044
Published
Sep 10, 2026
Updated
Sep 10, 2026
Vendor
The Netty Project
Product
Netty
Classifications
T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.1.133.Final <4.1.138.Final
  2. Affected versionversion=4.2.13.Final <4.2.18.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Netty Project · Nettyversion=4.1.133.Final <4.1.138.Final; version=4.2.13.Final <4.2.18.Final

Published CVSS scores

6.5GitHub Security AdvisoryCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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