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A GitHub-reviewed security advisory, not necessarily under active exploitation the way our CISA KEV advisories are, but a real, disclosed vulnerability in an open-source dependency.
Affected packages
Vulnerable: <= 6.6.0
Patched in 6.6.1
Details
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.
EPSS, exploit probability
Low0.16%
estimated chance of real-world exploitation in the next 30 days, higher than 5.6% of every CVE FIRST.org scores
Refreshed 11/14/2026, via FIRST.org's EPSS model, not CVSS, this measures likelihood of exploitation, not how severe it would be.
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