tornadoweb Tornado up to 6.5 Cookie RequestHandler.set_cookie max_age injection

Summaryinfo

A vulnerability, which was classified as critical, was found in tornadoweb Tornado up to 6.5. This issue affects the function RequestHandler.set_cookie of the component Cookie Handler. Executing a manipulation of the argument max_age can lead to injection. This vulnerability is registered as CVE-2026-123535. It is possible to launch the attack remotely. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in tornadoweb Tornado up to 6.5. It has been declared as critical. This vulnerability affects the function RequestHandler.set_cookie of the component Cookie Handler. The manipulation of the argument max_age with an unknown input leads to a injection vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

Tornado before 6.6 does not validate the max_age argument of RequestHandler.set_cookie (also called by set_signed_cookie, set_secure_cookie, and clear_cookie), allowing injection of additional Set-Cookie attributes. When an application passes attacker-influenced input as max_age, an attacker can embed attributes such as Domain, Path, or Secure to widen the cookie's scope to parent paths or other subdomains.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-123535 since 11/06/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1055.

Upgrading to version 6.6 eliminates this vulnerability.

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Productinfo

Vendor

• tornadoweb

Name

• Tornado

Version

• 6.0
• 6.1
• 6.2
• 6.3
• 6.4
• 6.5

Website

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

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