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.
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.002 (16.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 16.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.002 · change: -0.000
Affected products
Weakness classification (CWE)
References
- github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x (vendor-advisory)
- www.vulncheck.com/advisories/tornado-before-6.5.8-cookie-attribute-injection-vi… (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.