CVE-2026-116578

Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, tornado.web.RedirectHandler URL templates can place regex-capture substitutions where crafted request paths change the redirect scheme or network location. Affected placements include substitutions at the start of a path, directly after a fixed host, or at the beginning of the template, including protocol-relative, absolute, backslash, encoded, host-extension, and user-info variants interpreted by browsers as attacker-controlled destinations. Static templates and substitutions after a fixed host followed by a slash are not affected. An attacker can use the resulting open redirect on the application's domain for phishing. This issue is fixed in version 6.6.

• https://github.com/tornadoweb/tornado/commit/940ea725bdd9bc68231d68a105eef17ea6e11233
• https://github.com/tornadoweb/tornado/commit/cc75ab0eb3af459c714895a49f682ad354f50117
• https://github.com/tornadoweb/tornado/commit/ccb6a2e5482f17997efd4a74b8200d5b4babc035
• https://github.com/tornadoweb/tornado/pull/3786
• https://github.com/tornadoweb/tornado/releases/tag/v6.6.0
• https://github.com/tornadoweb/tornado/security/advisories/GHSA-pw9p-v7r6-gx4p