Public proof of conceptFix available

CVE-2026-42578

Q: Is CVE-2026-42578 actively exploited?

A proof-of-concept exploit exists for CVE-2026-42578, but active exploitation has not been confirmed at this time.

Q: What is the CVSS score for CVE-2026-42578?

CVE-2026-42578 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

A public proof of concept exists; no exploitation attested.

Published2026-05-13
Fixed in4.2.13 · 4.1.133
WeaknessCWE-113 · CWE-93

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC

2026-05-1319:17CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-42578?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-42578?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV

Netty

Branch	Affected	Fixed in	Source
4.2	≥ 4.2.0, < 4.2.13	4.2.13	NVD
4.1	< 4.1.133	4.1.133	NVD

netty-handler-proxy

Branch	Affected	Fixed in	Source
4.2	≥ 4.2.0.Alpha1, < 4.2.13.Final	4.2.13.Final	OSV
4.1	< 4.1.133.Final	4.1.133.Final	OSV

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

RHSA-2026:76128 Red Hat Product Security3 products fixed
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 7
RHSA-2026:76130 Red Hat Product Security3 products fixed
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 9
RHSA-2026:76129 Red Hat Product Security3 products fixed
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 8
RHSA-2026:76134 Red Hat Product Security3 products fixed
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 for OpenShift image security update
RHSA-2026:76132 Red Hat Product Security1 product fixed
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update
RHSA-2026:69459 Red Hat Product Security1 product fixed
Red Hat Security Advisory: AMQ Clients 2026.Q3

8 more advisories

Full record on NVD

Fix

Update Netty to 4.2.13 · 4.1.133
Vendor fix Red Hat Product Security RHSA-2026:76128 · 3 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Vendor fix Red Hat Product Security RHSA-2026:76134 · 3 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Vendor fix Red Hat Product Security RHSA-2026:76132 · 1 productBefore applying the update, back up your existing installation, including all applications, configuration files, databases and database settings, and so on. The References section of this erratum contains a download link (you must log in to download the update).
Vendor fix Red Hat Product Security RHSA-2026:66545 · 1 productBefore applying the update, back up your existing installation, including all applications, configuration files, databases and database settings. The References section of this erratum contains a download link (you must log in to download the update).
Vendor fix Red Hat Product Security RHSA-2026:53806 · 1 productBefore applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://acce…
Vendor fix Red Hat Product Security RHSA-2026:36820 · 4 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258

Advisories and patches

github.comMitigation · Vendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionpoc2026-05-13
OpenCVESSVC decisionpoc—
CNACVSS 4.02.9read 2026-10-23
CNACVSS 3.17.5read 2026-10-23
NVDCVSS 3.17.5read 2026-10-23
CNAweakness (CWE)CWE-113, CWE-93read 2026-10-23
FIRST EPSSEPSS score1.2 %2026-10-22
OSVaffected packages—

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS 4.0 vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published: 2026-05-13
Last Modified: 2026-09-18
NVD status: Modified

Frequently asked questions

What is CVE-2026-42578?

Is CVE-2026-42578 actively exploited?

A proof-of-concept exploit exists for CVE-2026-42578, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-42578?

CVE-2026-42578 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

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