CVE-2026-59900Network attack vector

Routing bypass via duplicate Host header translation

Published Jul 29, 2026 · Updated Jul 29, 2026

HTTP request smuggling in Netty before 4.1.136.Final and 4.2.0.Final through 4.2.15.Final allows remote attackers to bypass request routing. Http2StreamFrameToHttpObjectCodec and InboundHttp2ToHttpAdapter map :authority to Host while also copying a supplied host header, leaving two attacker-controlled Host values in one HttpRequest. Exposure requires an affected translator and a downstream component that resolves the duplicate values differently, allowing virtual-host or policy selection to diverge.

CVSS severity6.9
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in Netty before 4.1.136.Final and 4.2.0.Final through 4.2.15.Final allows remote attackers to bypass request routing. Http2StreamFrameToHttpObjectCodec and InboundHttp2ToHttpAdapter map :authority to Host while also copying a supplied host header, leaving two attacker-controlled Host values in one HttpRequest. Exposure requires an affected translator and a downstream component that resolves the duplicate values differently, allowing virtual-host or policy selection to diverge.

The record

CVE
CVE-2026-59900
Published
Jul 29, 2026
Updated
Jul 29, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 29, 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=< 4.1.136.Final
  2. Affected versionversion=>= 4.2.0.Final, < 4.2.16.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Netty Project · Nettyversion=< 4.1.136.Final; version=>= 4.2.0.Final, < 4.2.16.Final

Published CVSS scores

6.9GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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