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Advisory record · GHSA-mgf9-4vpg-hj56

tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)

CVSS 7.5 HighEPSS 0.0057 · 47th percentile

Published by the GitHub Advisory Database at 15 Jun 2026, 20:19 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
tornadoPyPI<6.5.66.5.6
Identifiers
GHSA-mgf9-4vpg-hj56 · CVE-2026-49855 · PYSEC-2026-3389
Weakness (CWE)
CWE-409
Tags
Published
15 Jun 2026
Updated
10 Sept 2026

Machine-written summary

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

Tornado versions before 6.5.6 are vulnerable to a gzip decompression bomb: the gzip decompression code has no overall limit on the total decompressed size, only on the compressed size. A malicious server that a client connects to via SimpleAsyncHTTPClient in its default configuration can make it consume effectively unlimited memory. Upgrade tornado to 6.5.6 or later; before upgrading, set decompress_response to False or use CurlAsyncHTTPClient.

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
7.5 High 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0057, the 47th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:11 UTC First seen by agentprime
  2. 31 Oct 2026, 14:11 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.