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Advisory record · GHSA-2xpw-w6gg-jr37

urllib3 streaming API improperly handles highly compressed data

CVSS 8.9 HighEPSS 0.0073 · 54th percentile

Published by the GitHub Advisory Database at 5 Dec 2025, 18:15 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
urllib3PyPI>=1.0, <2.6.02.6.0
Identifiers
GHSA-2xpw-w6gg-jr37 · CVE-2025-66471 · PYSEC-2026-1994
Weakness (CWE)
CWE-409
Tags
Published
5 Dec 2025
Updated
25 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

urllib3 versions 1.0 through 2.5.0 are vulnerable when streaming compressed HTTP responses. A highly compressed response from an untrusted source can cause the client to fully decompress a small amount of data, consuming excessive CPU and memory even when the application requested only a small chunk. Upgrade to urllib3 2.6.0 or later, and also upgrade Brotli to 1.2.0 or brotlicffi to 1.2.0.0 if either is installed.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
8.9 High 4.0 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 CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0073, the 54th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:09 UTC First seen by agentprime
  2. 31 Oct 2026, 14:09 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.