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.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact Low

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact Low

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
tornadoweb tornado unaffected
Version Status Constraints
0 affected < 6.5.9
6.5.9 unaffected —

No data.

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Project Subscriptions

Vendors Products
Tornadoweb Subscribe
Tornado Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/tornadoweb/tornado/commit/03945136ea9746eccf61caf88edae39642e59c93 cve-icon cve-icon
https://github.com/tornadoweb/tornado/security/advisories/GHSA-3hv7-mjh2-fv65 cve-icon cve-icon
https://www.vulncheck.com/advisories/tornado-before-6.5.9-denial-of-service-via-query-string cve-icon cve-icon
History

Thu, 01 Oct 2026 11:00:00 +0000

Type Values Removed Values Added
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.
Title Tornado before 6.5.9 Denial of Service via Query String
First Time appeared Tornadoweb
Tornadoweb tornado
Weaknesses CWE-770
CPEs cpe:2.3:a:tornadoweb:tornado:*:*:*:*:*:*:*:*
Vendors & Products Tornadoweb
Tornadoweb tornado
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

cvssV4_0

{'score': 6.9, 'vector': '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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-10-01T10:42:04.230Z

Reserved: 2026-09-30T10:55:39.869Z

Link: CVE-2026-103261

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-10-01T11:17:20.847

Modified: 2026-10-01T11:17:20.997

Link: CVE-2026-103261

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses