High 8.9Published Dec 5, 2025

CVE-2025-66418urllib3 allows an unbounded number of links in the decompression chain

Updated under an hour ago (Oct 28, 2026, 11:40 AM ET)

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Every CVE for urllib3

Exploited in the last 30 days

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.

CVSS: 8.9 HIGH (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
Weakness (CWE): CWE-770
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Dec 5, 2025
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

urllib3 urllib3 urllib3:urllib3 (from the name)	from 1.24, < 2.6.0	CNA record
python urllib3 python:urllib3	from 1.24 before 2.6.0	NVD

References

References

https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53	x-refsource-confirm, vendor-advisory
https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8	x-refsource-misc, patch

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.