CVE-2016-4970 is a high-severity (CVSS 7.5) CWE-835 vulnerability in io.netty:netty-handler. EPSS puts its 30-day exploitation probability at 11.3% (96th percentile). A fix is available for io.netty:netty-handler — see the affected versions and patch details below.
Loop with Unreachable Exit Condition in Netty
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-2016-4970 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 10–50% 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-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
handler/ssl/OpenSslEngine.java in Netty 4.0.x before 4.0.37.Final and 4.1.x before 4.1.1.Final allows remote attackers to cause a denial of service (infinite loop).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-handler | ≥ 4.0.0.Alpha1&&< 4.0.37.Final | 4.0.37.Finalio.netty:netty-handler:4.0.37.Final |
| ☕Maven | io.netty:netty-handler | ≥ 4.1.0.Beta1&&< 4.1.1.Final | 4.1.1.Finalio.netty:netty-handler:4.1.1.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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-handler to 4.0.37.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-4970 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-2016-4970 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2016-4970. 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.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Fuse 7.7.0 | netty | RHSA-2020:3192 |
| Red Hat JBoss A-MQ 6.3 | see advisory | RHSA-2017:0179 |
| Red Hat JBoss Data Grid 7.1 | see advisory | RHSA-2017:1097 |
Frequently Asked Questions
Is CVE-2016-4970 in your dependencies?
O3 Security finds CVE-2016-4970 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.