Quick answers
- Is CVE-2026-31958 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-31958 being exploited in the wild.
- How severe is CVE-2026-31958?
- High severity, with a CVSS score of 7.5, published 12 March 2026.
- Which products and versions are affected?
- tornado (PyPI) <= 6.5.4, ECOSYSTEM:introduced=0,fixed=6.5.5.
- Is there a fix for CVE-2026-31958?
- Yes. tornado (PyPI): upgrade to 6.5.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-31958 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-31958?
- Check whether you run tornado (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- tornado (PyPI): upgrade to 6.5.5 or later
pip install "tornado>=6.5.5"
Technical details
In Tornado versions prior to 6.5.5, the multipart/form-data parser lacks a limit on the number of parts allowed in a request, constrained only by the overall 'max_body_size'. Because parsing occurs synchronously on the main event loop thread, an attacker can submit a request with a very large number of small parts to consume excessive CPU cycles. This results in a denial-of-service (DoS) condition by blocking the main thread. The vulnerability is addressed in version 6.5.5 by introducing a default limit of 100 parts per request and providing new configuration options via 'tornado.httputil.ParseMultipartConfig'.
Affected products
- TornadoWeb Tornado <= 6.5.4
Identifiers
- CVE-2026-31958
- GHSA-qjxf-f2mg-c6mc
- PYSEC-2026-140
Timeline
- 2026-03-10: disclosed: Vulnerability published to tornadoweb/tornado repository
- 2026-03-11: advisory: Published to NVD
- 2026-03-12: advisory: Published to GitHub Advisory Database
- 2026-03-12: patched: Version 6.5.5 released