{"cve":"CVE-2025-66418","nvd":{"published":"2025-12-05T16:15:51.053","modified":"2026-09-25T23:10:00.463","status":"Analyzed","description":"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_v4":{"vector":"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","score":8.9},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-770"],"references":["https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8","https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53"],"products":["python:urllib3"],"source":"nvd","synced_at":"2026-10-19T22:16:40.427100871+00:00"},"epss":{"cve":"CVE-2025-66418","score":0.00682,"percentile":0.52479,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-gm62-xv2j-4w53","url":"https://osv.dev/vulnerability/GHSA-gm62-xv2j-4w53","summary":"urllib3 allows an unbounded number of links in the decompression chain","modified":"2026-09-10T03:50:58.741847479Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.24 <2.6.0"],"fixed":["2.6.0"]}]},{"id":"PYSEC-2026-1998","url":"https://osv.dev/vulnerability/PYSEC-2026-1998","summary":"urllib3 allows an unbounded number of links in the decompression chain","modified":"2026-07-07T17:47:54.140852492Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.24 <2.6.0"],"fixed":["2.6.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}