What is CVE-2026-91991?

CVE-2026-91991 is a medium-severity vulnerability in Tornadoweb Tornado, classified under HTTP Response Splitting. CVSS score: 5.4/10. Published 2026-09-15.

How severe is CVE-2026-91991?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Vulnerability in Tornadoweb Tornado

CVE-2026-91991

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 v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N.

Affected products

Tornadoweb Tornado

Weakness classification (CWE)

CWE-113 — HTTP Response Splitting

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (third-party-advisory)

Frequently asked questions

What is CVE-2026-91991?: CVE-2026-91991 is a medium-severity vulnerability in Tornadoweb Tornado, classified under HTTP Response Splitting. CVSS score: 5.4/10. Published 2026-09-15.
How severe is CVE-2026-91991?: Medium severity. CVSS v3 base score is 5.4 out of 10.