CVE-2026-103261

Tornado before 6.5.9 Denial of Service via Query String

State: Published
Severity: 6.9 Medium
Published: Oct 1, 2026
Updated: Oct 1, 2026
Reserved: Sep 30, 2026

Description

Tornado before 6.5.9 fails to limit the number of query string fields in HTTPServerRequest.__init__, allowing remote attackers to cause event-loop stalling by sending requests with thousands of query parameters. Attackers can send unauthenticated GET requests with unbounded query-string field counts to degrade response times for all clients sharing the same IOLoop.

Scores

CVSS	Score	Vector	Source
4.0	6.9 Medium	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	VulnCheck
3.1	5.3 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L	VulnCheck

Weaknesses

CWE-770 Allocation of Resources Without Limits or Throttling

Affected Products

Product	Versions
tornadotornadoweb	before 6.5.9Affected 6.5.9Not affected

References

GitHub Security Advisory (GHSA-3hv7-mjh2-fv65)vendor-advisory
https://github.com/tornadoweb/tornado/commit/03945136ea9746eccf61caf88edae39642e59c93patch
VulnCheck Advisory: Tornado before 6.5.9 Denial of Service via Query Stringthird-party-advisory

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