Bug 2561069 (CVE-2026-116577)

Summary:	CVE-2026-116577 tornado: tornado: Denial of Service via obsolete HTTP header line folding
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, anpicker, aos-team-art-private, asdas, bbrownin, dpaolell, dschmidt, ebourniv, eglynn, hasun, ikhan, jdelft, jfula, jjoyce, jlanda, jowilson, jpretori, jschluet, jupierce, jwong, kaycoth, kshier, lgarciaa, lhh, mbiarnes, mburns, mgarciac, nyancey, omaciel, ometelka, ppalepu, ppostler, prdhamdh, ptisnovs, rbobbitt, rhel-process-autobot, sbunciak, sghai, sidsharm, simaishi, stcannon, suppawar, syedriko, ttakamiy, vlaad, watson-tool-maintainers, xdharmai, yguenane
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in Tornado. An unauthenticated remote attacker can cause a Denial of Service (DoS) by sending crafted HTTP requests containing many folded header continuation lines. Processing these lines requires quadratic computational effort, consuming excessive CPU resources on the server's event loop and blocking legitimate incoming connections.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-10-26 20:32:08 UTC

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.