CVE-2026-91991

Name	CVE-2026-91991
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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1148323

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
python-tornado (PTS)	bookworm, bookworm (security)	6.2.0-3+deb12u4	vulnerable
	trixie (security), trixie	6.4.2-3+deb13u2	fixed
	forky, sid	6.5.5-5	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
python-tornado	source	trixie	(not affected)
python-tornado	source	(unstable)	(unfixed)			1148323

Notes

[trixie] - python-tornado <not-affected> (Incomplete fix for CVE-2026-35536 not applied)
https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889x
CVE exists because of an incomplete fix for CVE-2026-35536