---
id: "CVE-2026-116578"
kind: "vulnerability"
aliases: ["CVE-2026-116578"]
title: "Tornado: RedirectHandler templates let crafted paths send users to other sites"
severity: "low"
cvss: 2.1
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["package", "python", "self-hosted", "tornado"]
not_affected_if: ["no-redirecthandler", "static-redirect-templates", "upgraded-to-6.6"]
published_at: "2026-10-26T21:18:14+00:00"
first_seen_at: "2026-10-26T21:20:31+00:00"
updated_at: "2026-10-26T21:21:20+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116578", "first_seen_at": "2026-10-26T21:20:31+00:00"}]
---

# Tornado: RedirectHandler templates let crafted paths send users to other sites

Tornado's RedirectHandler can be given URL templates with regex-capture substitutions in positions that let a crafted request path change the redirect scheme or host. An attacker gets an open redirect on the application's own domain, usable for phishing.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `pip show tornado` or `python -c "import tornado; print(tornado.version)"` to read the installed version
- Search the codebase for `RedirectHandler` and check whether any URL template starts with a regex capture group, or places one directly after a fixed host

## Fix

- Upgrade tornado to `6.6` or later
- Where upgrading is not possible, make redirect templates static or keep a slash after any fixed host before a capture group

## Timeline

- 2026-10-26T21:20:31+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-116578

## From the sources

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.

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