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.
Affected products
tornadoweb: tornado
References3
- github.com/tornadoweb/tornado/security/advisories/GHSA-pr2v-jx2… MitigationVendor Advisory
- github.com/tornadoweb/tornado/commit/9c163aebeaad9e6e7d28bac1f3… Patch
- github.com/tornadoweb/tornado/releases/tag/v6.5.3 Release Notes
Metrics
- CVSS 3.1
-
6.1
MEDIUM
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - EPSS — exploit probability
- 0% percentile: 15 · as of 11 November 2026
- CWE
- CWE-79CWE-644
Could this be exploited in your environment?
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