CVE-2026-91991

EUVD-2026-78663
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.
HTTP Request/Response Splitting
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
VulnCheckCNA
5.4 MEDIUM
NETWORK
HIGH
NONE
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: Unknown
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
tornadowebtornado
6.5.5 ≤
𝑥
< 6.5.8
CNA
Debian logo
Debian Releases
Debian Product
Codename
python-tornado
bookworm
vulnerable
bookworm (security)
vulnerable
forky
vulnerable
sid
vulnerable
trixie
6.4.2-3+deb13u2
fixed
trixie (security)
6.4.2-3+deb13u2
fixed
Common Weakness Enumeration
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