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Advisory record · GHSA-38jv-5279-wg99

Decompression-bomb safeguards bypassed when following HTTP redirects (streaming API)

CVSS 8.9 HighEPSS 0.029 · 87th percentile

Published by the GitHub Advisory Database at 7 Jan 2026, 19:18 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
urllib3PyPI>=1.22, <2.6.32.6.3
Identifiers
GHSA-38jv-5279-wg99 · CVE-2026-21441 · PYSEC-2026-1996
Weakness (CWE)
CWE-409
Tags
Published
7 Jan 2026
Updated
10 Sept 2026

Machine-written summary

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

urllib3 1.22 and later, before 2.6.3, decompresses redirect response bodies when streaming with preload_content=False and redirects enabled. A malicious server can exploit this decompression bomb to cause high CPU and memory use on the client. Upgrade to urllib3 2.6.3, or set redirect=False for requests to untrusted sources.

Written 5 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 0.029, the 87th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:34 UTC First seen by agentprime
  2. 31 Oct 2026, 14:34 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.