CVE-2021-21419 is a medium-severity (CVSS 5.3) Uncontrolled Resource Consumption vulnerability in eventlet. A fix is available for eventlet — see the affected versions and patch details below.
Improper Handling of Highly Compressed Data (Data Amplification) and Memory Allocation with Excessive Size Value in eventlet
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-2021-21419 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 378,567 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
eventletReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
A websocket peer may exhaust memory on Eventlet side by sending very large websocket frames. Malicious peer may exhaust memory on Eventlet side by sending highly compressed data frame.
Patches
Version 0.31.0 restricts websocket frame to reasonable limits.
Workarounds
Restricting memory usage via OS limits would help against overall machine exhaustion. No workaround to protect Eventlet process.
For more information
If you have any questions or comments about this advisory:
- Open an issue in eventlet
- Contact current maintainers. At 2021-03: [email protected] or https://t.me/temotor
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | eventlet | ≥ 0.10&&< 0.31.0 | 0.31.0pip install --upgrade 'eventlet==0.31.0' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for eventlet, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update eventlet to 0.31.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21419 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-2021-21419 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-21419. 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 4, the python-eventlet package is only used in Ironic container images, used for Baremetal provisioning, and Kuryr SDN container images, used for deployments on OpenStack. * In Red Hat Gluster Storage 3, python-eventlet package was primarily shipped as a dependency of openstack-swift.…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenShift Container Platform 4.8 | python-eventlet-0:0.25.2-4.el8 | RHSA-2021:2437 |
| Red Hat OpenStack Platform 16.1 | python-eventlet-0:0.25.2-5.el8ost.1 | RHSA-2021:5071 |
Frequently Asked Questions
Is CVE-2021-21419 in your dependencies?
O3 Security finds CVE-2021-21419 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.