high7.5
CVE-2026-31958
Tornado is vulnerable to DoS due to too many multipart parts
Impact
In versions of Tornado prior to 6.5.5, the only limit on the number of parts in `multipart/form-data` is the `max_body_size` setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. Tornado 6.5.5 introduces new limits on the size and complexity of multipart bodies, including a default limit of 100 parts per request. These limits are configurable if needed; see `tornado.httputil.ParseMultipartConfig`. It is also now possible to disable `multipart/form-data` parsing entirely if it is not required for the application.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | tornado | <= 6.5.4 | 6.5.5 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Tornadoweb | Tornado | before 6.5.5 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-qjxf-f2mg-c6mc
- https://lists.debian.org/debian-lts-announce/2026/04/msg00000.html
- https://github.com/advisories/GHSA-qjxf-f2mg-c6mc
- https://nvd.nist.gov/vuln/detail/CVE-2026-31958
- https://github.com/tornadoweb/tornado/commit/119a195e290c43ad2d63a2cf012c29d43d6ed839
- https://github.com/tornadoweb/tornado/releases/tag/v6.5.5
- https://github.com/pypa/advisory-database/tree/main/vulns/tornado/PYSEC-2026-140.yaml