CVE-2026-91991

MEDIUM 5.4

Tornado before 6.5.8 Cookie Attribute Injection via Capitalized kwargs

CVSS Score

5.4

EPSS Score

0.0%

EPSS Percentile

0th

Tornado before 6.5.8 contains an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by passing capitalized or legacy keyword arguments to set_cookie. Attackers can embed semicolon-delimited data in capitalized parameters like Domain, Path, or SameSite to bypass validation and modify cookie security attributes.

CWE	CWE-113
Vendor	tornadoweb
Product	tornado
Published	Sep 15, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Affected Versions

tornadoweb / tornado

6.5.5 < 6.5.8

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x vulncheck.com: https://www.vulncheck.com/advisories/tornado-before-6.5.8-cookie-attribute-injection-via-capitalized-kwargs

Credits

🔍 sec-reex 🔍 arpitjain099