Netty up to 4.1.133.Final/4.2.13.Final newInitialMessage response splitting

CVSS Meta Temp Score
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CTI Interest Score
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6.3$0-$5k0.00

Summaryinfo

A vulnerability classified as problematic was found in Netty up to 4.1.133.Final/4.2.13.Final. Affected is the function newInitialMessage. Such manipulation leads to response splitting. This vulnerability is uniquely identified as CVE-2026-42578. The attack can be launched remotely. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Netty up to 4.1.133.Final/4.2.13.Final. Affected by this issue is the function newInitialMessage. The manipulation with an unknown input leads to a response splitting vulnerability. Using CWE to declare the problem leads to CWE-113. The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers. Impacted is integrity. CVE summarizes:

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty's HttpProxyHandler constructs HTTP CONNECT requests with header validation explicitly disabled. The newInitialMessage() method creates headers using DefaultHttpHeadersFactory.headersFactory().withValidation(false), then adds user-provided outboundHeaders without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-42578 since 04/28/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 314888 (Linux Distros Unpatched Vulnerability : CVE-2026-42578), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 4.1.133.Final or 4.2.13.Final eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (314888). Once again VulDB remains the best source for vulnerability data.

Productinfo

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Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 6.4
VulDB Meta Temp Score: 6.3

VulDB Base Score: 5.3
VulDB Temp Score: 5.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 7.5
NVD Vector: 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Response splitting
CWE: CWE-113 / CWE-93 / CWE-74
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Proof-of-Concept

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 314888
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2026-42578

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Netty 4.1.133.Final/4.2.13.Final

Timelineinfo

04/28/2026 CVE reserved
05/13/2026 +15 days Advisory disclosed
05/13/2026 +0 days VulDB entry created
05/19/2026 +6 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-42578 (🔒)
GCVE (CVE): GCVE-0-2026-42578
GCVE (VulDB): GCVE-100-363692

Entryinfo

Created: 05/13/2026 20:52
Updated: 05/19/2026 09:32
Changes: 05/13/2026 20:52 (33), 05/13/2026 20:53 (33), 05/15/2026 09:04 (2), 05/19/2026 09:32 (13)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

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