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Python tornado: Tornado before 6.5.9 fails to limit the number of query string fields in HTTPServerRequest.__init__, allowing remote attackers to cause event-loop… (CVE-2026-103261)

0
Medium
VulnerabilityCVE-2026-103261gcveosvubuntu-cve-2026-103261cve-2026-103261ubuntu-pro-16-04-ltsubuntu-pro-18-04-ltsubuntu-pro-20-04-ltsubuntu-pro-22-04-ltsubuntu-24-04-ltsubuntu-26-10ubuntu-26-04-lts
Published: 10/01/2026 (10/01/2026, 11:17:00 UTC)
Source: GCVE Database
Product: python-tornado

Description

Python Tornado versions before 6.5.9 do not limit the number of query string fields in HTTPServerRequest.__init__. This allows remote attackers to send unauthenticated GET requests with thousands of query parameters, causing event-loop stalling and degrading response times for all clients sharing the same IOLoop.

CVSS v3.1

Score 5.3medium

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected software

Ubuntu:Pro:16.04:LTSmore threats →ghsa
python-tornado
pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-infra-legacy/xenial
Affected versions
=4.2.1-1ubuntu2=4.2.1-1ubuntu3=4.2.1-1ubuntu3.1=4.2.1-1ubuntu3.1+esm1=4.2.1-1ubuntu3.1+esm2=4.2.1-1ubuntu3.1+esm3=4.2.1-1ubuntu3.1+esm4
Ubuntu:Pro:18.04:LTSmore threats →ghsa
python-tornado
pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps/bionic
Affected versions
=4.5.1-2.1~build2=4.5.2-1=4.5.3-1=4.5.3-1ubuntu0.1=4.5.3-1ubuntu0.2=4.5.3-1ubuntu0.2+esm1=4.5.3-1ubuntu0.2+esm2=4.5.3-1ubuntu0.2+esm3=4.5.3-1ubuntu0.2+esm4
Ubuntu:Pro:20.04:LTSmore threats →ghsa
python-tornado
pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps/focal
Affected versions
=5.1.1-4ubuntu1=5.1.1-4ubuntu5=6.0.3+really5.1.1-2=6.0.3+really5.1.1-2build1=6.0.3+really5.1.1-2build2=6.0.3+really5.1.1-3=6.0.3+really5.1.1-3ubuntu0.1~esm1=6.0.3+really5.1.1-3ubuntu0.1~esm3=6.0.3+really5.1.1-3ubuntu0.1~esm5=6.0.3+really5.1.1-3ubuntu0.1~esm7
Ubuntu:Pro:22.04:LTSmore threats →ghsa
python-tornado
pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps/jammy
Affected versions
=6.1.0-1build1=6.1.0-2=6.1.0-3=6.1.0-3build1=6.1.0-3ubuntu0.1~esm1=6.1.0-3ubuntu0.1~esm2=6.1.0-3ubuntu0.1~esm4=6.1.0-3ubuntu0.1~esm5=6.1.0-3ubuntu0.1~esm6
Ubuntu:24.04:LTSmore threats →ghsa
python-tornado
pkg:deb/ubuntu/python-tornado?arch=source&distro=noble
Affected versions
=6.3.2-1=6.4.0-0ubuntu1=6.4.0-1=6.4.0-1build1=6.4.0-1ubuntu0.1=6.4.0-1ubuntu0.2=6.4.0-1ubuntu0.4=6.4.0-1ubuntu0.5=6.4.0-1ubuntu0.6
Ubuntu:26.10more threats →ghsa
python-tornado
pkg:deb/ubuntu/python-tornado?arch=source&distro=stonking
Affected versions
=6.5.4-0.1=6.5.5-2=6.5.5-4=6.5.5-5=6.5.5-5ubuntu1.1
Ubuntu:26.04:LTSmore threats →ghsa
python-tornado
pkg:deb/ubuntu/python-tornado?arch=source&distro=resolute
Affected versions
=6.4.2-3=6.5.2-3=6.5.4-0.1=6.5.4-0.1ubuntu0.1=6.5.4-0.1ubuntu0.2

Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.

AI-Powered Analysis

Machine-generated threat intelligence

AILast updated: 10/22/2026, 17:23:55 UTC

Technical Analysis

The vulnerability in Python Tornado prior to version 6.5.9 involves the failure to limit the number of query string fields processed in the HTTPServerRequest.__init__ method. Remote attackers can exploit this by sending GET requests with an unbounded number of query parameters, which causes the Tornado event loop to stall. This results in degraded response times for all clients using the same IOLoop, effectively causing a denial-of-service condition.

Potential Impact

An attacker can cause event-loop stalling by sending requests with thousands of query parameters, leading to degraded response times for all clients sharing the same IOLoop. This impacts availability but does not affect confidentiality or integrity.

Mitigation Recommendations

A fix is available in Tornado version 6.5.9. Users should upgrade to version 6.5.9 or later to remediate this vulnerability.

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Technical Details

Gcve Source
db.gcve.eu
Osv Id
UBUNTU-CVE-2026-103261
Osv Schema Version
1.7.0
Ecosystems
["Ubuntu:Pro:16.04:LTS","Ubuntu:Pro:18.04:LTS","Ubuntu:Pro:20.04:LTS","Ubuntu:Pro:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:26.10","Ubuntu:26.04:LTS"]
Cvss Version
3.1
State
PUBLISHED

Threat ID: 6ada44d64d27ba8daa6a512f

Added to database: 10/22/2026, 17:16:06 UTC

Last enriched: 10/22/2026, 17:23:55 UTC

Last updated: 10/22/2026, 17:23:55 UTC

Views: 2

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