What’s Vulnerable › Vulnerabilities

CVE-2026-91991: Tornado before 6.5.8 Cookie Attribute Injection via Capitalized kwargs

• Severity: medium (CVSS 5.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-15 · updated 2026-10-08
• Weakness: CWE-113

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.

Affected products

• tornadoweb tornado: from 6.5.5 before 6.5.8 — fixed in 6.5.8

How to fix

Upgrade to a fixed version: tornadoweb tornado 6.5.8. Check the vendor advisory for mitigations.

References

• https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x
• https://www.vulncheck.com/advisories/tornado-before-6.5.8-cookie-attribute-injection-via-capitalized-kwargs
• https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x

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