Tornado: Open redirect in RedirectHandler via protocol-relative URLs

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.1 · 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 · score source

EPSS

• CVE-2026-116578: 0.46% estimated exploitation activity in the next 30 days; percentile 39.79 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary `tornado.web.RedirectHandler` builds its target URL by substituting parts of the request path into a template. Depending on where those substitutions appear in the template, an attacker can craft a request that redirects to a host of their choosing. This creates an open redirect on the application's domain, which can be used in phishing.

Impact Applications are affected if they use `RedirectHandler` with a URL template where a regex capture group can influence the scheme or host of the redirect. This includes: - A substitution at the start of the path, for example `(r"/(.*)/target", RedirectHandler, {"url": "/{0}/destination"})`. A request to `https://example.com//evil.com/target` redirects to `//evil.com/destination`, a protocol-relative URL pointing to evil.com. Variants using backslashes or encoded characters have the same effect, because browsers treat them as equivalent to `//`. - A substitution directly after the host, for example `(r"/old(.*)",…

Published by the source

28 Oct 2026, 22:43 UTC

Last modified by the source

28 Oct 2026, 23:00 UTC

Source last checked

29 Oct 2026, 06:10 UTC

1. Revision 2 · amended · 29 Oct 2026

   Amended from osv record GHSA-pw9p-v7r6-gx4p

2. Revision 1 · created · 28 Oct 2026

   Published from ghsa record GHSA-pw9p-v7r6-gx4p

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# Patch Next advisory brief: CVE-2026-116578

Advisory: Tornado: Open redirect in RedirectHandler via protocol-relative URLs
IDs: CVE-2026-116578, GHSA-pw9p-v7r6-gx4p
Record: https://patchnext.com/advisories/cve-2026-116578 (revision 2, source checked 29 Oct 2026, 06:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tornado 6.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI tornado: affected < 6.6; fixed in 6.6

## Suggested inspection (read-only)
- `python -m pip show tornado`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on tornado.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-pw9p-v7r6-gx4p (OSV record GHSA-pw9p-v7r6-gx4p lists affected ranges: PyPI tornado >=0 <6.6 (fixed))
- Verified: https://github.com/advisories/GHSA-pw9p-v7r6-gx4p (GitHub-reviewed advisory GHSA-pw9p-v7r6-gx4p lists affected ranges: PyPI tornado >=0 <6.6)

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