CVE-2026-116577

Medium

Description

Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, Tornado's HTTP header parser accepts obsolete line folding and repeatedly concatenates short continuation lines, causing quadratic CPU consumption on the IOLoop thread. An unauthenticated client can submit a header block containing many obsolete line-folding continuations before application code runs, blocking other connections served by the process. The cost grows with max_header_size, and only availability is affected. This issue is fixed in version 6.6.

SeverityMedium

CVSS5.3

Exploit probability—

ProductTornado

PublishedOct 26, 2026

First seenOct 26, 2026

Weakness typeCWE-407CWE-407 CWE-770Allocation of resources without limits

How to fix

Update

tornado6.6 or later

Affected products

Product	Affected versions	Fixed in
tornadoPyPI	v < 6.6	6.6

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