CVE-2025-67724 — Tornado vulnerable to Header Injection and XSS via reason argument

Affected: tornadoweb tornado

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.

USN-7950-1 — python-tornado vulnerabilities

Affected: Ubuntu:Pro:16.04:LTS: python-tornado, Ubuntu:Pro:18.04:LTS: python-tornado, Ubuntu:Pro:20.04:LTS: python-tornado, Ubuntu:Pro:22.04:LTS: python-tornado, Ubuntu:24.04:LTS: python-tornado, Ubuntu:25.10: python-tornado

It was discovered that Tornado incorrectly handled special characters in HTTP headers. An attacker could possibly use this issue to execute a cross- site scripting (XSS) attack. This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Ubuntu 25.04, and Ubuntu 25.10. (CVE-2025-67724)

It was discovered that Tornado incorrectly handled repeated HTTP headers. An attacker could possibly use this issue to cause Tornado to use excessive resources, causing a denial of service. (CVE-2025-67725)

It was discovered that Tornado incorrectly handled parsing of certain HTTP header values. An attacker could possibly use this issue to cause Tornado to use excessive resources, causing a denial of service. (CVE-2025-67726)

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CVE-2025-67724 — Tornado vulnerable to Header Injection and XSS via reason argument

USN-7950-1 — python-tornado vulnerabilities