CVE-2025-67724

Tornado vulnerable to Header Injection and XSS via reason argument

State: Published
Severity: 5.4 Medium
Published: Dec 12, 2025
Updated: Dec 18, 2025
Reserved: Dec 10, 2025

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.

Scores

CVSS	Score	Vector	Source
3.1	5.4 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N	GitHub_M

Weaknesses

CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-644 Improper Neutralization of HTTP Headers for Scripting Syntax

Affected Products

Product	Versions
tornadotornadoweb	< 6.5.3Affected

References

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