Description
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.
References6
- github.com/tornadoweb/tornado/commit/940ea725bdd9bc68231d68a105…
- github.com/tornadoweb/tornado/commit/cc75ab0eb3af459c714895a49f…
- github.com/tornadoweb/tornado/commit/ccb6a2e5482f17997efd4a74b8…
- github.com/tornadoweb/tornado/pull/3786
- github.com/tornadoweb/tornado/releases/tag/v6.6.0
- github.com/tornadoweb/tornado/security/advisories/GHSA-pw9p-v7r…
Metrics
- CVSS 4.0
-
2.1
LOW
Score source: CNA
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 40 · as of 8 November 2026
- CWE
- CWE-601
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.