{"cve":"CVE-2025-66471","nvd":{"published":"2025-12-05T17:16:04.400","modified":"2026-09-25T23:10:00.463","status":"Analyzed","description":"urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.0 and prior to 2.6.0, the Streaming API improperly handles highly compressed data. urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When streaming a compressed response, urllib3 can perform decoding or decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). The library must read compressed data from the network and decompress it until the requested chunk size is met. Any resulting decompressed data that exceeds the requested amount is held in an internal buffer for the next read operation. The decompression logic could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This can result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data.","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-409"],"references":["https://github.com/urllib3/urllib3/commit/c19571de34c47de3a766541b041637ba5f716ed7","https://github.com/urllib3/urllib3/security/advisories/GHSA-2xpw-w6gg-jr37"],"products":["python:urllib3"],"source":"nvd","synced_at":"2026-10-19T22:16:40.427100871+00:00"},"epss":{"cve":"CVE-2025-66471","score":0.00682,"percentile":0.52471,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-2xpw-w6gg-jr37","url":"https://osv.dev/vulnerability/GHSA-2xpw-w6gg-jr37","summary":"urllib3 streaming API improperly handles highly compressed data","modified":"2026-09-25T17:15:05.968189421Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.0 <2.6.0"],"fixed":["2.6.0"]}]},{"id":"PYSEC-2026-1994","url":"https://osv.dev/vulnerability/PYSEC-2026-1994","summary":"urllib3 streaming API improperly handles highly compressed data","modified":"2026-07-07T17:48:15.379954669Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.0 <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."]}