---
id: CVE-2026-91990
title: >-
  Tornado before 6.5.8 contains a memory amplification vulnerability in
  parse_multipart_form_data that splits multipart data before validating the
  max_parts limit
summary: >-
  Tornado before 6.5.8 contains a memory amplification vulnerability in
  parse_multipart_form_data that splits multipart data before validating the
  max_parts limit. Attackers can send crafted multipart requests with many parts
  to create lar…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-770
vendor: tornadoweb
product: tornado
affected:
  - tornado < 6.5.8
published: '2026-09-15'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T13:42:49.167'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-91990'
references:
  - url: >-
      https://github.com/tornadoweb/tornado/security/advisories/GHSA-8423-8fgw-73vq
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/tornado-before-6.5.8-memory-amplification-dos-via-multipart
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/tornadoweb/tornado/security/advisories/GHSA-8423-8fgw-73vq
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/tornadoweb/tornado/pull/3704'
  - url: >-
      https://github.com/tornadoweb/tornado/commit/de85b3f87446e323e881bbaa3d5a74f4b76e5f05
  - url: 'https://gist.github.com/afldl/649861f25d39b53b7edbe0298e171617'
  - url: 'https://github.com/tornadoweb/tornado'
  - url: 'https://github.com/tornadoweb/tornado/releases/tag/v6.5.8'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-91990.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-91990'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2533953'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-91990'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-91990'
tags:
  - nvd
  - cve.org
  - exploit-available
  - osv
  - pip
  - csaf
  - vex
  - red-hat
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-15T16:04:53.956684Z'
ingestedAt: '2026-09-15T15:39:12.909Z'
aliases:
  - GHSA-8423-8fgw-73vq
ecosystem: pip
patched:
  - tornado 6.5.8
epss: 0.00412
epssPercentile: 0.35222
---

## Overview

Tornado before 6.5.8 contains a memory amplification vulnerability in parse_multipart_form_data that splits multipart data before validating the max_parts limit. Attackers can send crafted multipart requests with many parts to create large transient lists, exhausting server memory and causing denial of service.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-91990)

Affected packages:

- `tornado < 6.5.8`

Patched in:

- `tornado 6.5.8`

Source: https://osv.dev/vulnerability/GHSA-8423-8fgw-73vq

## Vendor advisories

- **Red Hat VEX** · Important · affected: Exploit Intelligence, Lightspeed Core, Migration Toolkit for Applications 8, OpenShift Lightspeed, Red Hat Ansible Automation Platform 2, Red Hat Enterprise Linux 10, … · no fix planned: Exploit Intelligence, Lightspeed Core, Migration Toolkit for Applications 8, OpenShift Lightspeed, … · updated 2026-09-17 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-91990.json)