What’s Vulnerable › Vulnerabilities

CVE-2021-21419: Improper Handling of Highly Compressed Data (Data Amplification) and Memory Allocation with Excessive Size Value in eventlet

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-05-07 · updated 2026-06-17
• Weakness: CWE-400

Description

Eventlet is a concurrent networking library for Python. 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. A patch in version 0.31.0 restricts websocket frame to reasonable limits. As a workaround, restricting memory usage via OS limits would help against overall machine exhaustion, but there is no workaround to protect Eventlet process.

Affected products

• eventlet: from 0.10 before 0.31.0 — fixed in 0.31.0
• Fedoraproject Fedora: 33, 34

How to fix

Upgrade to a fixed version: eventlet 0.31.0. Check the vendor advisory for mitigations.

References

• https://github.com/eventlet/eventlet/security/advisories/GHSA-9p9m-jm8w-94p2
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2WJFSBPLCNSZNHYQC4QDRDFRTEZRMD2L/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/R5JZP4LZOSP7CUAM3GIRW6PIAWKH5VGB/
• https://github.com/eventlet/eventlet/security/advisories/GHSA-9p9m-jm8w-94p2
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2WJFSBPLCNSZNHYQC4QDRDFRTEZRMD2L/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/R5JZP4LZOSP7CUAM3GIRW6PIAWKH5VGB/

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