Description
Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, the supplied reason phrase is used unescaped in HTTP headers (where it could be used for header injection) or in HTML in the default error page (where it could be used for XSS) and can be exploited by passing untrusted or malicious data into the reason argument. Used by both RequestHandler.set_status and tornado.web.HTTPError, the argument is designed to allow applications to pass custom "reason" phrases (the "Not Found" in HTTP/1.1 404 Not Found) to the HTTP status line (mainly for non-standard status codes). This issue is fixed in version 6.5.3.
References (3)
Core 3
Core References
Mitigation, Vendor Advisory x_refsource_confirm
https://github.com/tornadoweb/tornado/security/advisories/GHSA-pr2v-jx2c-wg9f
Patch x_refsource_misc
https://github.com/tornadoweb/tornado/commit/9c163aebeaad9e6e7d28bac1f33580eb00b0e421
Release Notes x_refsource_misc
https://github.com/tornadoweb/tornado/releases/tag/v6.5.3
Scores
CVSS v3
5.4
EPSS
0.0008
EPSS Percentile
22.9%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
CISA SSVC
Vulnrichment
Exploitation
none
Automatable
no
Technical Impact
partial
Details
CWE
CWE-644
CWE-79
Status
published
Products (1)
tornadoweb/tornado
< 6.5.3
Published
Dec 12, 2025
Tracked Since
Feb 18, 2026