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Response snapshot Oct 29, 2026, 02:31 UTC

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VulnerabilityCVE-2026-116578

Tornado: Open redirect in RedirectHandler via protocol-relative URLs

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.

At a glance

Exploited
Not known
Severity
2.1 Low (CVSS 4.0)
Chance of exploitation
0.5% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: tornado: 6.6. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-pw9p-v7r6-gx4p (opens a new tab)

What happened

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:

Continue reading

- 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(.*)", RedirectHandler, {"url": "https://new.example.com{0}"}). A request to /old.evil.com/ or /old@evil.com/ redirects to evil.com. - A template that begins with a substitution (such as "{0}"), which can be given an absolute URL.

Applications are not affected if their RedirectHandler templates use only static URLs, or if every substitution comes after a fixed host and a / (for example "/static/{0}" or "https://example.com/{0}"). Other uses of RequestHandler.redirect() are not affected by this advisory, although applications that pass user-controlled input to redirect() should validate it themselves.

Patches

Fixed in Tornado 6.6. RedirectHandler now returns a 400 error if the substituted values would change the scheme or host of the redirect from what the template specifies. As a result, substitutions can no longer be used in the scheme or host part of a template. The similar check in StaticFileHandler has also been hardened against backslash and whitespace variants.

Workarounds

- Change RedirectHandler templates so every substitution comes after a fixed prefix ending in /, or write capture-group regexes that cannot match characters such as /, \, @, . or : where they could affect the host. - Alternatively, replace RedirectHandler with a custom handler that validates the target before calling self.redirect().

Credit

Reported by Longwei Wang (@gn00295120).

Affected package ranges reported by GitHub: tornado: < 6.6

Scores and how they were measured

CVSS base severity

2.1

Version 4.0As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.5%

Scored Percentile 39.7%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-pw9p-v7r6-gx4p (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-pw9p-v7r6-gx4p, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-116578, scored 2026-10-28. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). Tornado: Open redirect in RedirectHandler via protocol-relative URLs (CVE-2026-116578). https://kevwire.com/record/CVE-2026-116578

MLA

"Tornado: Open redirect in RedirectHandler via protocol-relative URLs (CVE-2026-116578)." KEVWire, 28 Oct. 2026, kevwire.com/record/CVE-2026-116578.

Chicago

KEVWire. "Tornado: Open redirect in RedirectHandler via protocol-relative URLs (CVE-2026-116578)." Last modified October 28, 2026. https://kevwire.com/record/CVE-2026-116578.

Evidence summary (plain text)

Tornado: Open redirect in RedirectHandler via protocol-relative URLs (Oct 28, 2026).
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.

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.
CVSS 2.1 (version 4.0; evidence as of Oct 28, 2026; https://github.com/advisories/GHSA-pw9p-v7r6-gx4p).
EPSS 0.5% for the following 30 days, scored Oct 28, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-116578&date=2026-10-28).
Sources:
GitHub-reviewed advisory GHSA-pw9p-v7r6-gx4p: https://github.com/advisories/GHSA-pw9p-v7r6-gx4p
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-116578&date=2026-10-28
Record ID: CVE-2026-116578.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 02:16 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

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