CVE-2026-91991 PUBLISHED

Tornado before 6.5.8 Cookie Attribute Injection via Capitalized kwargs

Assigner: VulnCheck
Reserved: 15.09.2026 Published: 15.09.2026 Updated: 15.09.2026

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:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
CVSS Score: 6.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	Low	Confidentiality	Low
Attack Complexity	High	Integrity	Low	Integrity	Low
Attack Requirements	Present	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
CVSS Score: 5.4

Attack Vector	Network	Scope	Changed
Attack Complexity	High	Confidentiality Impact	Low
Privileges Required	None	Integrity Impact	Low
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	tornadoweb
Product	tornado
Versions	Default: unaffected affected from 6.5.5 to 6.5.8 (excl.) Version 6.5.8 is unaffected

Credits

sec-reex reporter
arpitjain099 reporter

References

Problem Types

Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') CWE