GHSA-x4gw-5cx5-pgmh — netty-handler
HIGHGHSA-x4gw-5cx5-pgmh is a high-severity (CVSS 7.5) CWE-770 vulnerability in io.netty:netty-handler. A fix is available for io.netty:netty-handler — see the affected versions and patch details below.
Netty: SNI handler pre-allocates up to 16 MiB from nine attacker bytes
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-x4gw-5cx5-pgmh.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-x4gw-5cx5-pgmh by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
io.netty:netty-handler☕io.netty:netty-handlerReal-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 a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, SslClientHelloHandler.decode() reads the 24-bit TLS handshake length and, when the ClientHello does not fit in the first record, eagerly allocates ctx.alloc().buffer(handshakeLength) (line 161). The guard at line 140 is handshakeLength > maxClientHelloLength && maxClientHelloLength != 0, and the commonly-used SniHandler/AbstractSniHandler constructors (SniHandler(Mapping), SniHandler(AsyncMapping), AbstractSniHandler()) pass maxClientHelloLength=0 and handshakeTimeoutMillis=0, so the length guard is disabled and no timeout is scheduled. A 16 MiB request exceeds the default pooled chunk size and becomes a huge/unpooled allocation performed immediately. The buffer is retained in the handler until the channel closes. Versions 4.1.135.Final and 4.2.15.Final patch the issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-handler | ≥ 4.2.0.Final&&< 4.2.15.Final | 4.2.15.Finalio.netty:netty-handler:4.2.15.Final |
| ☕Maven | io.netty:netty-handler | all versions | 4.1.135.Finalio.netty:netty-handler:4.1.135.Final |
Affected Products
nettynettyDetection & 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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-handler to 4.2.15.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-x4gw-5cx5-pgmh is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
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 vulnerability in Netty is rated as Important. It allows a remote attacker to trigger a denial of service by sending a specially crafted TLS ClientHello message. The flaw arises from an eager, unbounded memory allocation during the TLS handshake, particularly when default configurations disable the maximum client…
To mitigate this issue, configure applications utilizing Netty's `SslClientHelloHandler` to specify a non-zero value for the `maxClientHelloLength` parameter. This will enable the internal length validation, preventing the eager allocation of large memory buffers when processing crafted TLS ClientHello messages. Refer to your specific application's documentation for details on configuring Netty's TLS handler. A restart of the affected application or service is required for the configuration changes to take effect.Source: Red Hat security advisory for GHSA-x4gw-5cx5-pgmh (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| AMQ Clients 2026.Q3 | netty-handler | RHSA-2026:69459 |
| Cryostat 4 on RHEL 9 | cryostat/cryostat-reports-rhel9:4.2.0-13 | RHSA-2026:48151 |
| Red Hat AMQ Broker 7.13.6 | netty-handler | RHSA-2026:66545 |
| Red Hat AMQ Broker 7.14.1 | netty-handler | RHSA-2026:66488 |
| Red Hat Build of Apache Camel 3.33 for Quarkus 3.33.2.SP1 | netty-handler | RHSA-2026:26586 |
| Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16 | netty-handler | RHSA-2026:37390 |
| Red Hat build of Quarkus 3.27.4.SP1 | netty-handler | RHSA-2026:26018 |
| Red Hat build of Quarkus 3.33.2.SP1 | netty-handler | RHSA-2026:26017 |
Frequently Asked Questions
Is GHSA-x4gw-5cx5-pgmh in your dependencies?
Find it across Maven, including transitive dependencies.