CriticalCVE-2026-42584

Netty: HttpClientCodec response desynchronization (CVE-2026-42584)

Published 13.05.2026Last modified 26.10.2026Sources: Red Hat, BSI, CVE.org, OSV, EUVD, SUSE, Ubuntu

Public exploit

What is affected, what to do

An exploit is publicly available. Update Netty to version 4.1.133.Final, Io.netty Netty-codec-http to version 4.1.133.Final.

Affected: Netty gte 4.2.0.Alpha1, < 4.2.13.Final..*
Netty lt *..4.1.133.Final
Io.netty Netty-codec-http gte 4.2.0.Alpha1, < 4.2.13.Final..*
Io.netty Netty-codec-http lt *..4.1.133.Final
Fixed in: Netty 4.1.133.Final
Io.netty Netty-codec-http 4.1.133.Final

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

9.1

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

9.1

CVSS v3

Severity Critical on the scale from 0 to 10.

Source: Red Hat, BSI, CVE.org, OSV, EUVD, SUSE, Ubuntu

0.8 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 57.6

Show all metrics

Severity: Critical
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 89.48 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: PoC (publicly reported)
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 9.1 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 9.1
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.8 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 57.6; High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 13.05.2026
CISA assessment (SSVC): Exploitation: proof of concept · automatable · Technical impact: partial; Source: CISA Vulnrichment, as of 13 May 2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-444, CWE-444

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpClientCodec pairs each inbound response with an outbound request by queue.poll() once per response, including for 1xx. If the client pipelines GET then HEAD and the server sends 103, then 200 with GET body, then 200 for HEAD, the queue pairs HEAD with the first 200. The HEAD rule then skips reading that message’s body, so the GET entity bytes stay on the stream and the following 200 is parsed from the wrong offset. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Source: redhat_csaf, BSI WID Portal, BSI CSAF, NVD (NIST), CVE.org (MITRE), cvelistv5, OSV (Open Source Vulnerabilities), ENISA EUVD, suse_csaf, Ubuntu Security Notices

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
io.netty	netty-codec-http	`≥ 4.2.0.Alpha1, < 4.2.13.Final` `< 4.1.133.Final`	— `4.1.133.Final`
netty	netty	`< 4.1.133.Final` `≥ 4.2.0.Alpha1, < 4.2.13.Final` `4.2.0 – < 4.2.13` `< 4.1.133`	`4.1.133.Final` — `4.2.13` `4.1.133`

Vendors and products

Weakness classes (CWE)

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Base
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Entry at MITRE CWE-444
CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Base
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Entry at MITRE CWE-444

Public exploit references

Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

Public exploit references

Reference tagged as exploit	github.com (opens in a new tab)	PoC (publicly reported)reported, not verified	—

References & sources

github.comnetty/netty/security/advisories/GHSA-57rv-r2g8-2cj3web, x_refsource_CONFIRM, Exploit, Vendor advisory
NVD (NIST)vuln/detail/CVE-2026-42584advisory
github.comnetty/nettypackage
access.redhat.comsecurity/cve/CVE-2026-42584Vulnerability database, x_refsource_REDHAT
bugzilla.redhat.comRHBZ#2477224Issue tracking, x_refsource_REDHAT
security.access.redhat.comdata/csaf/v2/vex/2026/cve-2026-42584.jsonx_sadp-csaf-vex
access.redhat.comerrata/RHSA-2026:53644Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:28010Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:53806Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:42644Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:25123Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:36820Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:37390Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:23808Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:24502Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:54435Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:49700Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:65126Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:66545Vendor advisory, x_refsource_REDHAT
access.redhat.comerrata/RHSA-2026:66488Vendor advisory, x_refsource_REDHAT

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

18.09.2026Record modifiedRed Hat ADP

New references:

Show 4 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/42xxx/CVE-2026-42584.json">CVE-2026-42584</a>
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:53645
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:53646
Reference	removed	https://access.redhat.com/errata/RHSA-2026:53806	—

Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

17.09.2026Record modifiedRed Hat ADP
New references:
- https://access.redhat.com/errata/RHSA-2026:49701
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Reference added
—
https://access.redhat.com/errata/RHSA-2026:49701
Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:49701

11.09.2026Record modifiedRed Hat ADP

New references:

Show 3 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/42xxx/CVE-2026-42584.json">CVE-2026-42584</a>
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:66488
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:66545

Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

09.09.2026Record modifiedRed Hat ADP

New references:

https://access.redhat.com/errata/RHSA-2026:65126

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/42xxx/CVE-2026-42584.json">CVE-2026-42584</a>
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:65126

Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

07.09.2026Record modifiedGitHub

New references:

https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3

Show 3 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3
Reference	removed	https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3	—
Reference type	removed	https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3 Types: Exploit, Vendor Advisory	—

Source identifier: security-advisories@github.com

Show 5 older changes

07.09.2026Record modifiedCISA ADP

New references:

https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3

Show 3 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3
Reference	removed	https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3	—
Reference type	removed	https://github.com/netty/netty/security/advisories/GHSA-57rv-r2g8-2cj3 Types: Exploit, Vendor Advisory	—

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

07.09.2026Record modifiedRed Hat ADP

New references:

and 8 more references

Show 28 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/42xxx/CVE-2026-42584.json">CVE-2026-42584</a>
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:23808
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:24502
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:25123
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:28010
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:36820
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:37390
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:42644
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:49700
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:53644
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:53806
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:54435
Reference	added	—	https://access.redhat.com/security/cve/CVE-2026-42584
Reference	added	—	https://bugzilla.redhat.com/show_bug.cgi?id=2477224
Reference	added	—	https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42584.json
Reference	removed	https://access.redhat.com/errata/RHSA-2026:23808	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:24502	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:25123	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:28010	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:36820	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:37390	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:42644	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:53644	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:53806	—
Reference	removed	https://access.redhat.com/errata/RHSA-2026:54435	—
Reference	removed	https://access.redhat.com/security/cve/CVE-2026-42584	—
Reference	removed	https://bugzilla.redhat.com/show_bug.cgi?id=2477224	—
Reference	removed	https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42584.json	—

Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

21.08.2026Record modifiedRed Hat ADP

1 individual change: Affected versions (publisher)

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	changed	Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9 (+70)	Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9 (+70)

Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

21.07.2026Record modifiedRed Hat ADP

New references:

https://access.redhat.com/errata/RHSA-2026:42644

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:42644
Affected versions (publisher)	changed	Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9 (+53)	Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9, Cryostat 4 on RHEL 9 (+53)

Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

09.07.2026Record modifiedRed Hat ADP

New references:

https://access.redhat.com/errata/RHSA-2026:36820

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://access.redhat.com/errata/RHSA-2026:36820
Affected versions (publisher)	changed	Cryostat 4 on RHEL 9, Red Hat OpenShift Dev Spaces 3.28, Red Hat build of Quarkus 3.27.4 (+24)	Cryostat 4 on RHEL 9, Red Hat OpenShift Dev Spaces 3.28, Red Hat OpenShift Dev Spaces 3.29 (+24)

Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

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<a href="https://intel.neosec.eu/en/cve/CVE-2026-42584"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-42584.svg?lang=en" alt="CVE-2026-42584 – NEOSEC Intel" height="20"></a>