Bug 2561044 (CVE-2026-115927)

Summary: CVE-2026-115927 tornado: Tornado: Denial of Service via chunked transfer encoding processing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, anpicker, aos-team-art-private, asdas, bbrownin, dpaolell, dschmidt, ebourniv, eglynn, hasun, 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, vlaad, watson-tool-maintainers, xdharmai, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Tornado. When decoding HTTP/1.1 chunked transfer encoding, Tornado processes received data without yielding control back to the event loop. A remote unauthenticated attacker can send requests containing a large volume of small chunks to monopolize the process and consume excessive memory. This issue leads to a Denial of Service (DoS), stalling all other connections handled by the affected process.
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Description OSIDB Bzimport 2026-10-26 19:52:02 UTC 
Tornado is a Python web framework and asynchronous networking library. Prior to 6.6.0, Tornado decodes HTTP/1.1 chunked transfer encoding by processing body data that has already arrived without yielding to the event loop. A remote unauthenticated peer can send millions of one-byte chunks to monopolize the process event loop and stall every other connection served by that process, while lowering max_body_size only limits the duration of each request. For handlers that do not use @stream_request_body, retaining each chunk as a separate object can consume roughly twenty times the received body size, and SimpleAsyncHTTPClient has the same event-loop behavior when reading a response from a malicious server. This issue is fixed in version 6.6.0.