CVE-2026-91991
Published:September 15, 2026
Updated:September 22, 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.
Affected Packages
tornado (CONDA):
Affected version(s) >=6.5.5 <6.5.8Fix Suggestion:
Update to version 6.5.8https://github.com/tornadoweb/tornado.git (GITHUB):
Affected version(s) >=v6.5.5 <v6.5.8Fix Suggestion:
Update to version v6.5.8tornado (PYTHON):
Affected version(s) >=6.5.5 <6.5.8Fix Suggestion:
Update to version 6.5.8Related Resources (2)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.3
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
LOW
Vulnerable System Integrity
LOW
Vulnerable System Availability
NONE
Subsequent System Confidentiality
LOW
Subsequent System Integrity
LOW
Subsequent System Availability
NONE
CVSS v3
Base Score:
5.4
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Weakness Type (CWE)
Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
EPSS
Base Score:
0.22