🛡️ CVE-2026-49854 — tornado

🟡 CVSS 5.3 — Medium ✅ No Known Exploit CWE-126 NVD
5.3
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Tornado has out-of-bounds memory access via C extension

Summary

Tornado's optional native extension tornado.speedups implements websocket_mask without validating that the mask argument is exactly four bytes long. The C function reads four bytes from mask unconditionally, even when Python passes a shorter byte string. This can read beyond the provided buffer, exposing up to 3 bytes of uninitialized memory.

The behavior is reachable from Tornado's XSRF token decoder when xsrf_cookies=True and the native extension is active.

Mitigations

This bug is fixed in Tornado 6.5.6. Prior to upgrading to this version, setting the environment variable TORNADO_EXTENSION=0 will disable the vulnerable code (at the expense of reducing websocket performance).

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality low, integrity none, availability none.

Affected software

CVE-2026-49854 is recorded against 2 packages.

  • tornado (fixed in 6.5.6)
  • unknown

Timeline and source

Published on 12 June 2026 and last revised on 13 July 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
github.com (Package)
github.com (Web)

Details

Severity LOW
CVSS Score 5.3
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
CWE CWE-126
Public Exploit ✅ No
Source NVD
Published 2026-06-12
Updated 2026-08-12
Modified 2026-07-13
Fix URL N/A

Affected Packages

Software From version Fixed in
tornado — 6.5.6
unknown — —

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