CVE-2021-43797 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.
HTTP request smuggling 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-2021-43797 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 377,636 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☕org.jboss.netty:netty☕io.netty:nettyReal-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 for rapid development of maintainable high performance protocol servers & clients. Netty prior to version 4.1.71.Final skips control chars when they are present at the beginning / end of the header name. It should instead fail fast as these are not allowed by the spec and could lead to HTTP request smuggling. Failing to do the validation might cause netty to "sanitize" header names before it forward these to another remote system when used as proxy. This remote system can't see the invalid usage anymore, and therefore does not do the validation itself. Users should upgrade to version 4.1.71.Final.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-http | ≥ 4.0.0&&< 4.1.71.Final | 4.1.71.Finalio.netty:netty-codec-http:4.1.71.Final |
| ☕Maven | org.jboss.netty:netty | all versions | No fix |
| ☕Maven | io.netty:netty | all versions | No fix |
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 4.1.71.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43797 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-2021-43797 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-43797. 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.
In OpenShift Container Platform (OCP), the Hive/Presto/Hadoop components that comprise the OCP Metering stack, ship the vulnerable version of netty-codec-http package. Since the release of OCP 4.6, the Metering product has been deprecated, hence the affected components are marked as wontfix. The…
| Product | Fixed in | Advisory |
|---|---|---|
| Logging subsystem for Red Hat OpenShift 5.4 | openshift-logging/elasticsearch6-rhel8:v6.8.1-156 | RHSA-2022:2216 |
| OpenShift Logging 5.2 | openshift-logging/elasticsearch6-rhel8:v6.8.1-157 | RHSA-2022:2218 |
| OpenShift Logging 5.3 | openshift-logging/elasticsearch6-rhel8:v6.8.1-159 | RHSA-2022:2217 |
| Red Hat AMQ 7.10.0 | netty | RHSA-2022:5101 |
| Red Hat AMQ Streams 2.1.0 | netty | RHSA-2022:1345 |
| Red Hat build of Quarkus 2.7.5 | netty | RHSA-2022:4623 |
| Red Hat Data Grid 8.3.0 | netty | RHSA-2022:0520 |
| Red Hat Fuse 7.11 | netty | RHSA-2022:5532 |
Frequently Asked Questions
Is CVE-2021-43797 in your dependencies?
O3 Security finds CVE-2021-43797 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.