CVE-2026-126347 Tornado: Open redirect via triple-slash redirect paths
Attackers can craft triple-slash redirect destinations in Tornado apps using URL templates to send users to attacker-controlled hosts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Harmful if only installed
- No
- Needs a specific call
- Yes
- Fix
- None listed
What is CVE-2026-126347?
CVE-2026-126347 is a low-severity open redirect vulnerability in tornadoweb tornado, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Tornado is a Python web framework and asynchronous networking library. In versions through 6.6.0, applications using tornado.web.RedirectHandler with URL templates that allow attacker-controlled substitutions to influence the destination can be vulnerable to an open redirect using three or more leading slashes. Differences between Python’s URL parsing and browser URL interpretation allow a crafted destination to redirect a user to an attacker-controlled host. The remediation for CVE-2026-116578 in version 6.6.0 did not fully address this case. This issue is fixed in version 6.6.1.
Weakness: CWE-601
Which versions are affected by CVE-2026-126347?
An affected version is only exploitable if your software calls tornado.web.RedirectHandler. Many projects that include it are not exposed.
How do I fix CVE-2026-126347?
No fix has been published for CVE-2026-126347 yet. Limit exposure of the affected software until one is available.
Upgrade, and only redirect to addresses on an allow-list. More about Open redirect.
Is CVE-2026-126347 being exploited?
There is no known exploitation of CVE-2026-126347 in the wild and no public exploit code.
Sources
Also known as GHSA-5cjw-f85j-cv6r.