Quick answers
- Is CVE-2026-49854 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-49854 being exploited in the wild.
- How severe is CVE-2026-49854?
- Medium severity, with a CVSS score of 5.3, published 14 July 2026.
- Which products and versions are affected?
- tornado (PyPI) < 6.5.6, ECOSYSTEM:introduced=0,fixed=6.5.6.
- Is there a fix for CVE-2026-49854?
- Yes. tornado (PyPI): upgrade to 6.5.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-49854 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-49854?
- 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 6.5.6 or later
pip install "tornado>=6.5.6"
Technical details
A buffer over-read vulnerability (CWE-126) exists in Tornado's optional C extension, tornado.speedups. The websocket_mask function fails to validate that the mask argument is exactly four bytes long, leading the underlying C function to read up to three bytes beyond the provided buffer. This vulnerability is reachable via the XSRF token decoding process when xsrf_cookies is enabled and the native extension is active. An unauthenticated remote attacker can exploit this to read small amounts of uninitialized memory. The issue is resolved in version 6.5.6; users can mitigate the risk by setting TORNADO_EXTENSION=0 to disable the native extension.
Affected products
- Tornadoweb Tornado < 6.5.6
Identifiers
- CVE-2026-49854
- GHSA-cx3h-4qpv-8hc9
- PYSEC-2026-3388
Timeline
- 2026-05-27: patched: Version 6.5.6 released
- 2026-05-27: advisory: GitHub Security Advisory published
- 2026-07-14: disclosed: CVE published to NVD