Medium severity · published Sep 15, 2026
CVE-2026-91991
Tornado before 6.5.8 Cookie Attribute Injection via Capitalized kwargs
5.4
CVSS
0.2%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 16% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
TO
tornado · tornadoweb
6.5.5 before 6.5.8 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-91991
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-91991
vendor-advisory
https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x
third-party-advisory
https://www.vulncheck.com/advisories/tornado-before-6.5.8-cookie-attribute-injection-via-capitalized-kwargs
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