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Not in CISA KEV
LOW severity

Tornado: Open redirect via triple-slash redirect pathsGHSA-5cjw-f85j-cv6r

LOWFix: tornadoweb/tornado@c503241

GHSA-5cjw-f85j-cv6r is a low-severity (CVSS 3.1) Open Redirect vulnerability in tornado. A fix is available for tornado — see the affected versions and patch details below.

Also known asCVE-2026-126347
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 13, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs6th percentile — riskier than 6% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐍tornado

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPItornadoall versions6.6.1pip install --upgrade 'tornado==6.6.1'

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tornado, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update tornado to 6.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-5cjw-f85j-cv6r is resolved across your whole dependency graph.

  3. Workarounds

    Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.

Frequently Asked Questions

### Summary Due to differences in the way browsers and Python's `urllib` parse urls, browsers treat a string starting with three or more slashes as a protocol-level redirect, while `urllib` does not. This means that the 6.6.0 fix for the RedirectHandler open redirect (CVE-2026-116578, commit cc75ab0e) is incomplete. Tornado 6.6.1 improves the open-redirect detection to handle this case correctly, as well as fixing a regression in the 6.6.0 implementation.
O3 Security · Impact-Aware SCA

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Tornado: Open redirect via triple-slash redirect paths