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  5. GHSA-8423-8fgw-73vq

GHSA-8423-8fgw-73vq: tornado: multipart split() creates huge temp list before max_parts check -> memory amplification DoS (httputil.py:34)

September 1, 2026

parse_multipart_form_data (httputil.py:34) calls data.split(b"--"+boundary+b"\r\n") before the max_parts check (:35). A 600KB body with 100k parts creates a 100k-element transient list first, then rejects transient memory amplification (each split element is a copy). Pre-auth HTTP DoS.

References

  • gist.github.com/afldl/649861f25d39b53b7edbe0298e171617
  • github.com/advisories/GHSA-8423-8fgw-73vq
  • github.com/tornadoweb/tornado/commit/de85b3f87446e323e881bbaa3d5a74f4b76e5f05
  • github.com/tornadoweb/tornado/pull/3704
  • github.com/tornadoweb/tornado/releases/tag/v6.5.8
  • github.com/tornadoweb/tornado/security/advisories/GHSA-8423-8fgw-73vq

Code Behaviors & Features

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Affected versions

All versions before 6.5.8

Fixed versions

  • 6.5.8

Solution

Upgrade to version 6.5.8 or above.

Impact 5.3 MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Learn more about CVSS

Weakness

  • CWE-770: Allocation of Resources Without Limits or Throttling

Source file

pypi/tornado/GHSA-8423-8fgw-73vq.yml

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