CVE-2021-37136 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in io.netty:netty-codec. A fix is available for io.netty:netty-codec — see the affected versions and patch details below.
Bzip2Decoder doesn't allow setting size restrictions for decompressed data
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-2021-37136 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 378,156 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☕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
Impact
The Bzip2 decompression decoder function doesn't allow setting size restrictions on the decompressed output data (which affects the allocation size used during decompression).
All users of Bzip2Decoder are affected. The malicious input can trigger an OOME and so a DoS attack
Workarounds
No workarounds other than not using the Bzip2Decoder
References
Relevant code areas:
https://github.com/netty/netty/blob/netty-4.1.67.Final/codec/src/main/java/io/netty/handler/codec/compression/Bzip2Decoder.java#L80 https://github.com/netty/netty/blob/netty-4.1.67.Final/codec/src/main/java/io/netty/handler/codec/compression/Bzip2Decoder.java#L294 https://github.com/netty/netty/blob/netty-4.1.67.Final/codec/src/main/java/io/netty/handler/codec/compression/Bzip2Decoder.java#L305
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec | all versions | 4.1.68.Finalio.netty:netty-codec:4.1.68.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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-codec to 4.1.68.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-37136 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-2021-37136 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-37136. 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 the OpenShift Container Platform (OCP), the Hive/Presto/Hadoop components that comprise the OCP Metering stack ship the vulnerable version of netty-codec package. Since the release of OCP 4.6, the Metering product has been deprecated [1], so the affected components are marked as wontfix. This may be fixed in 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 5.1 | openshift-logging/elasticsearch6-rhel8:v6.8.1-67 | RHSA-2021:5128 |
| OpenShift Logging 5.2 | openshift-logging/elasticsearch6-rhel8:v6.8.1-66 | RHSA-2021:5127 |
| OpenShift Logging 5.2 | openshift-logging/elasticsearch6-rhel8:v6.8.1-157 | RHSA-2022:2218 |
| OpenShift Logging 5.3 | openshift-logging/elasticsearch6-rhel8:v6.8.1-65 | RHSA-2021:5129 |
| OpenShift Logging 5.3 | openshift-logging/elasticsearch6-rhel8:v6.8.1-159 | RHSA-2022:2217 |
| Red Hat AMQ 7.9.1 | netty-codec | RHSA-2021:4851 |
| Red Hat AMQ Streams 2.0.0 | netty-codec | RHSA-2022:0138 |
Frequently Asked Questions
Is CVE-2021-37136 in your dependencies?
O3 Security finds CVE-2021-37136 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.