CVE-2026-42578Public exploitNetwork attack vector

HTTP header injection via disabled CONNECT validation

Published May 13, 2026 · Updated May 13, 2026

HTTP header injection in Netty before 4.1.133.Final or 4.2.13.Final allows attackers to alter CONNECT requests via crafted headers. HttpProxyHandler.newInitialMessage() disables validation in its header factory and adds outboundHeaders without rejecting CRLF sequences. Exploitation requires an application to pass attacker-controlled headers without its own sanitization, enabling injected headers or a smuggled request to reach its proxy.

CVSS severity7.5
High
EPSS probability1.06%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP header injection in Netty before 4.1.133.Final or 4.2.13.Final allows attackers to alter CONNECT requests via crafted headers. HttpProxyHandler.newInitialMessage() disables validation in its header factory and adds outboundHeaders without rejecting CRLF sequences. Exploitation requires an application to pass attacker-controlled headers without its own sanitization, enabling injected headers or a smuggled request to reach its proxy.

The record

CVE
CVE-2026-42578
Published
May 13, 2026
Updated
May 13, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-113
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 13, 2026CVE publishedPublication date reported by the CVE source.
  2. May 13, 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
  2. Affected versionversion=>= 4.2.0.Alpha1, < 4.2.13.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Netty Project · Nettyversion=< 4.1.133.Final; version=>= 4.2.0.Alpha1, < 4.2.13.Final

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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 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

CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

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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