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Vulnerability · Published Jul 14, 2026 · Assigned by GitHub_M

CVE-2026-49854Tornado: Out-of-bounds memory access in C extension

Medium 5.3

In plain English

A medium-severity security flaw in tornado from tornadoweb. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.4%top 63.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.6, the optional native extension tornado.speedups implemented websocket_mask without validating that the mask argument is exactly four bytes, allowing the C function to read up to three bytes beyond the provided buffer when reached through Tornado XSRF token decoding with the native extension active. This issue is fixed in version 6.5.6.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12python-tornadono fix listedDEBIAN-CVE-2026-49854
Debian:13python-tornadono fix listedDEBIAN-CVE-2026-49854
Debian:14python-tornadono fix listedDEBIAN-CVE-2026-49854
PyPItornado6.5.6GHSA-cx3h-4qpv-8hc9
PyPItornado6.5.6PYSEC-2026-3388
Ubuntu:24.04:LTSpython-tornadono fix listedUBUNTU-CVE-2026-49854
Ubuntu:26.04:LTSpython-tornadono fix listedUBUNTU-CVE-2026-49854
Ubuntu:26.10python-tornadono fix listedUBUNTU-CVE-2026-49854

Affected products (as reported)

VendorProductVersions
tornadoweb tornado < 6.5.6

Weakness: CWE-126 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

References