TornadoWeb Tornado up to 6.5.7 Cookie set_cookie Domain/Path/SameSite injection

Summaryinfo

A vulnerability has been found in TornadoWeb Tornado up to 6.5.7 and classified as critical. This issue affects the function set_cookie of the component Cookie. The manipulation of the argument Domain/Path/SameSite leads to injection. This vulnerability is traded as CVE-2026-91991. It is possible to initiate the attack remotely. There is no exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as critical, has been found in TornadoWeb Tornado up to 6.5.7. This issue affects the function set_cookie of the component Cookie. The manipulation of the argument Domain/Path/SameSite with an unknown input leads to a injection vulnerability. Using CWE to declare the problem leads to CWE-74. The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-91991 since 09/15/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1055 for this issue.

Upgrading to version 6.5.8 eliminates this vulnerability.

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Productinfo

Vendor

• TornadoWeb

Name

• Tornado

Version

• 6.5.0
• 6.5.1
• 6.5.2
• 6.5.3
• 6.5.4
• 6.5.5
• 6.5.6
• 6.5.7

Website

• Product: https://github.com/tornadoweb/tornado/

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