---
id: CVE-2025-47287
aliases:
  - GHSA-7cx3-6m66-7c5m
  - PYSEC-2026-1974
title: >-
  Tornado vulnerable to excessive logging caused by malformed multipart form
  data
summary: >-
  Tornado vulnerable to excessive logging caused by malformed multipart form
  data
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'
vendor: tornado
product: tornado
ecosystem: pip
affected:
  - tornado < 6.5
patched:
  - tornado 6.5
published: '2025-05-16'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:24.284224963Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-7cx3-6m66-7c5m'
references:
  - url: >-
      https://github.com/tornadoweb/tornado/security/advisories/GHSA-7cx3-6m66-7c5m
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-47287'
  - url: >-
      https://github.com/tornadoweb/tornado/commit/b39b892bf78fe8fea01dd45199aa88307e7162f3
  - url: 'https://github.com/tornadoweb/tornado'
  - url: 'https://lists.debian.org/debian-lts-announce/2025/05/msg00038.html'
tags:
  - osv
  - pip
epss: 0.00741
epssPercentile: 0.5264
ingestedAt: '2026-07-08T18:25:46.981Z'
---

## Overview

### Summary

When Tornado's ``multipart/form-data`` parser encounters certain errors, it logs a warning but continues trying to parse the remainder of the data. This allows remote attackers to generate an extremely high volume of logs, constituting a DoS attack. This DoS is compounded by the fact that the logging subsystem is synchronous.

### Affected versions

All versions of Tornado prior to 6.5 are affected. The vulnerable parser is enabled by default.

### Solution

Upgrade to Tornado version 6.5. In the meantime, risk can be mitigated by blocking `Content-Type: multipart/form-data` in a proxy.

## Affected packages

- `tornado < 6.5`

## Remediation

Upgrade to a patched release:

- `tornado 6.5`