CVE-2026-42585 — netty-codec-http
MEDIUMCVE-2026-42585 is a medium-severity (CVSS 6.5) CWE-444 vulnerability in io.netty:netty-codec-http. A fix is available for io.netty:netty-codec-http — see the affected versions and patch details below.
Netty: HTTP Request Smuggling due to malformed Transfer-Encoding
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42585.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-42585 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
io.netty:netty-codec-http☕io.netty:netty-codec-httpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty incorrectly parses malformed Transfer-Encoding, enabling request smuggling attacks. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-http | ≥ 4.2.0.Alpha1&&< 4.2.13.Final | 4.2.13.Finalio.netty:netty-codec-http:4.2.13.Final |
| ☕Maven | io.netty:netty-codec-http | all versions | 4.1.133.Finalio.netty:netty-codec-http:4.1.133.Final |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-http, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-codec-http to 4.2.13.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42585 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-42585 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42585. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This Moderate flaw in Netty's HTTP codec allows for request smuggling attacks due to improper parsing of malformed Transfer-Encoding headers. An attacker could exploit this to bypass security controls, potentially leading to unauthorized access to sensitive information or manipulation of web traffic in Red Hat…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7 | eap7-activemq-artemis-0:2.16.0-22.redhat_00057.1.el7eap | RHSA-2026:53644 |
| Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 8 | eap7-activemq-artemis-0:2.16.0-22.redhat_00057.1.el8eap | RHSA-2026:53645 |
| Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 9 | eap7-activemq-artemis-0:2.16.0-22.redhat_00057.1.el9eap | RHSA-2026:53646 |
| Red Hat JBoss Enterprise Application Platform 8.1.7.GA | io.netty/netty-codec-http:4.1.135.Final-redhat-00001 | RHSA-2026:49701 |
| Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 10 | eap8-eap-product-conf-parent-0:801.7.1-1.GA_redhat_00001.1.el10eap | RHSA-2026:49700 |
Frequently Asked Questions
Is CVE-2026-42585 in your dependencies?
O3 Security finds CVE-2026-42585 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.