PYSEC-2026-1974
Tornado vulnerable to excessive logging caused by malformed multipart form data
At a glance
- Published
- Updated
- CVE
- CVE-2025-47287
- Aliases
- GHSA-7cx3-6m66-7c5m
- CVSS_V3
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Description
### 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
| Package | Versions |
|---|---|
| PyPI · tornado | introduced 0, fixed 6.5 |
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
Sources
| Source | Licence |
|---|---|
| OSV.dev | CC-BY 4.0 — PyPA Advisory Database |