CVE-2025-66418

urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.

Score

CVSS 4.0 8.9 High

Status

Analyzed - security-advisories@github.com

Published

2025-12-05

Last modified

2025-12-05

Weaknesses

CWE-770

Affected products

• Urllib3 (Python)
• Urllib3 (Urllib3)

References

• https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8
• https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53