CVE-2026-103261: Tornadoweb Tornado

Medium severity, CVSS 5.3. EPSS: 0.5% chance of exploitation in the next 30 days.

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.

Affected products

• Tornadoweb Tornado: before 6.5.9 (fixed in 6.5.9)

Published 2026-10-01. Last modified 2026-10-01.