GHSA-wwv5-g3v4-889x: tornado (CVE-2026-91991)

Package	Ecosystem	Affected	Fixed in
tornado	PyPI	>=6.5.5, <6.5.8	6.5.8

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Tornado versions 6.5.5 up to but not including 6.5.8 are affected. The set_cookie method's deprecated keyword-argument path does not validate attribute values, so a capitalized keyword such as Domain= or Path= can carry a semicolon and inject extra cookie attributes. An attacker who can influence those values in an app that uses this legacy keyword form could alter Secure, HttpOnly, SameSite, Domain or Path. Upgrade to Tornado 6.5.8.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
6.3	Medium	4.0	CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N	CNA (VulnCheck)

CISA KEV Not listed.
EPSS 0.0025, the 16th percentile, on 12 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:10 UTC First seen by agentprime
31 Oct 2026, 14:10 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.