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Tornado before 6.5.9 Denial of Service via Query String

CVSS 4.0 6.9 MEDIUMCVSS 3.1 5.3 MEDIUMCheck source for fixed versionsKEV status unknown

Historical advisory recorded 23 Oct 2026 15:48:27 UTC. Read the latest advisory.

cve-program · CVE-2026-103261

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-103261

Published

Tornado before 6.5.9 Denial of Service via Query String

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.

Source published
1 Oct 2026 10:42:04 UTC
Source modified
1 Oct 2026 14:44:26 UTC
Saved here
23 Oct 2026 15:48:27 UTC
Source terms
CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · 6.9 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

CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

ChangeIntel

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Sources read 12 Nov 16:29 UTC · 265 of 275 readable · 263 fully read · documentation 469/469 current