CVE-2025-67724

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.

Read the notes from the security team

• How can I get the fixes?
• What do statuses mean?
• Patch details

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Notes

Patch details

References

• MITRE
• NVD
• Launchpad
• Debian

Related Ubuntu Security Notices (USN)

• USN-7950-1
• Tornado vulnerabilities
• 8 January 2026

Other references

• https://www.cve.org/CVERecord?id=CVE-2025-67724
• https://github.com/tornadoweb/tornado/security/advisories/GHSA-pr2v-jx2c-wg9f
• https://github.com/tornadoweb/tornado/commit/9c163aebeaad9e6e7d28bac1f33580eb00b0e421
• https://github.com/tornadoweb/tornado/releases/tag/v6.5.3