GHSA-3hv7-mjh2-fv65: tornado (CVE-2026-103261)

Package	Ecosystem	Affected	Fixed in
tornado	PyPI	<6.5.9	6.5.9

Machine-written summary

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

Tornado versions before 6.5.9 parse URL query strings with no limit on the number of arguments, so a single request with thousands of short key=value pairs (within the header size limit) is processed in full. An unauthenticated remote attacker can send several such requests to stall Tornado's event loop and slow responses to other clients, a denial of service with no confidentiality or integrity impact. Upgrade to tornado 6.5.9 or later, which caps query-string arguments at the same 1000-field limit used for form bodies.

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
6.9	Medium	4.0	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N	CNA (VulnCheck)

CISA KEV Not listed.
EPSS 0.0047, the 40th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:09 UTC First seen by agentprime
31 Oct 2026, 14:09 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.