How severe is CVE-2021-21419?

CVE-2021-21419 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-21419?

CVE-2021-21419 affects the following packages: eventlet (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-21419?

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.

How do I detect CVE-2021-21419 in my PyPI dependencies?

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.

How do I mitigate CVE-2021-21419 if there is no patch (or I can't update yet)?

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.

Is CVE-2021-21419 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-21419 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-21419?

CVE-2021-21419 has an EPSS (Exploit Prediction Scoring System) score of 1.8%, placing it in the 79th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-21419?

CVE-2021-21419 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-21419 published, and has it been updated?

CVE-2021-21419 was published on May 7, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

MEDIUM severity

CVE-2021-21419 — eventlet

MEDIUMFix: eventlet/eventlet@1412f5e

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

Also known asGHSA-9p9m-jm8w-94p2PYSEC-2021-12

Published

May 7, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs79th percentile — riskier than 79% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍eventlet

Real-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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`eventlet`	≥ 0.10&&< 0.31.0	0.31.0`pip install --upgrade 'eventlet==0.31.0'`

Affected Products

2 products · 3 configurations

Application

eventleteventlet

≥ 0.10 && < 0.31.0

range

fedorafedoraproject

2 versions

3334

Detection & mitigation playbook

Open-source dependency

Detect
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
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.

Red HatModerate

* 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

### 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](https://github.com/eventlet/eventlet/issues) * Contact current main