PYSEC-2026-1974
Tornado vulnerable to excessive logging caused by malformed multipart form data
Quick fix
PYSEC-2026-1974 — tornado: upgrade to the fixed version with the command below.
pip install --upgrade 'tornado>=6.5'Details
### 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.
Are you affected?
Enter the version of the package you're using.
Affected packages
References
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-7cx3-6m66-7c5m[WEB]
- https://nvd.nist.gov/vuln/detail/CVE-2025-47287[ADVISORY]
- https://github.com/tornadoweb/tornado/commit/b39b892bf78fe8fea01dd45199aa88307e7162f3[WEB]
- https://github.com/tornadoweb/tornado[PACKAGE]
- https://lists.debian.org/debian-lts-announce/2025/05/msg00038.html[WEB]
- https://pypi.org/project/tornado[PACKAGE]
- https://github.com/advisories/GHSA-7cx3-6m66-7c5m[ADVISORY]