CVE-2026-42578 — netty-handler-proxy
CVE-2026-42578 is a CWE-113 vulnerability in io.netty:netty-handler-proxy. A fix is available for io.netty:netty-handler-proxy — see the affected versions and patch details below.
Netty: HTTP Header Injection via HttpProxyHandler Disabled Validation
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.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42578.
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.
Real-World Exposure
io.netty:netty-handler-proxy☕io.netty:netty-handler-proxyReal-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'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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-handler-proxy | all versions | 4.1.133.Finalio.netty:netty-handler-proxy:4.1.133.Final |
| ☕Maven | io.netty:netty-handler-proxy | ≥ 4.2.0.Alpha1&&< 4.2.13.Final | 4.2.13.Finalio.netty:netty-handler-proxy:4.2.13.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-handler-proxy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-handler-proxy to 4.1.133.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42578 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-2026-42578 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42578. 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.
Important: This vulnerability in Netty's HttpProxyHandler allows for HTTP header injection into CONNECT requests when an attacker can influence outbound headers. The handler's explicit disabling of header validation could enable proxy-related attacks, such as cache poisoning or bypassing security controls, impacting…
| Product | Fixed in | Advisory |
|---|---|---|
| Cryostat 4 on RHEL 9 | cryostat/cryostat-reports-rhel9:4.2.0-10 | RHSA-2026:28010 |
| Red Hat AMQ Broker 7.13.6 | netty-handler-proxy | RHSA-2026:66545 |
| Red Hat AMQ Broker 7.14.1 | netty-handler-proxy | RHSA-2026:66488 |
| Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16 | netty-handler-proxy | RHSA-2026:37390 |
| Red Hat build of Quarkus 3.27.4 | netty-handler-proxy | RHSA-2026:23808 |
| Red Hat build of Quarkus 3.33.2 | see advisory | RHSA-2026:24502 |
| 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 |
Frequently Asked Questions
Is CVE-2026-42578 in your dependencies?
O3 Security finds CVE-2026-42578 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.