PYSEC-2026-3388

See a problem?
Import Source
https://github.com/pypa/advisory-database/blob/main/vulns/tornado/PYSEC-2026-3388.yaml
JSON Data
https://api.osv.dev/v1/vulns/PYSEC-2026-3388
Aliases
Published
2026-07-13T15:46:17.044501Z
Modified
2026-07-13T16:33:26.790475442Z
Severity
  • 3.7 (Low) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N CVSS Calculator
Summary
Tornado has out-of-bounds memory access via C extension
Details

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).

References

Affected packages

PyPI / tornado

Package

Name
tornado
View open source insights on deps.dev
Purl
pkg:pypi/tornado

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
6.5.6

Affected versions

0.*
0.2
1.*
1.0
1.1
1.1.1
1.2
1.2.1
2.*
2.0
2.1
2.1.1
2.2
2.2.1
2.3
2.4
2.4.1
3.*
3.0
3.0.1
3.0.2
3.1
3.1.1
3.2
3.2.1
3.2.2
4.*
4.0
4.0.1
4.0.2
4.1b2
4.1
4.2b1
4.2
4.2.1
4.3b1
4.3b2
4.3
4.4b1
4.4
4.4.1
4.4.2
4.4.3
4.5b1
4.5b2
4.5
4.5.1
4.5.2
4.5.3
5.*
5.0a1
5.0b1
5.0
5.0.1
5.0.2
5.1b1
5.1
5.1.1
6.*
6.0a1
6.0b1
6.0
6.0.1
6.0.2
6.0.3
6.0.4
6.1b1
6.1b2
6.1
6.2b1
6.2b2
6.2
6.3b1
6.3
6.3.1
6.3.2
6.3.3
6.4b1
6.4
6.4.1
6.4.2
6.5b1
6.5
6.5.1
6.5.2
6.5.3
6.5.4
6.5.5

Database specific

source 
"https://github.com/pypa/advisory-database/blob/main/vulns/tornado/PYSEC-2026-3388.yaml"