Bug 2533964 (CVE-2026-91991)

Summary: CVE-2026-91991 tornado: Tornado: Cookie attribute injection via capitalized keyword arguments
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, anpicker, aos-team-art-private, asdas, bbrownin, bparees, 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, rhel-process-autobot, rjohnson, sbunciak, sghai, sidsharm, simaishi, stcannon, suppawar, syedriko, teagle, ttakamiy, 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. An attacker can bypass security validation in the `set_cookie` function by using capitalized or legacy keyword arguments. This allows the attacker to inject arbitrary cookie attributes, such as `Domain` or `SameSite`, and modify cookie security settings. The consequence is the potential to manipulate cookie behavior, which could lead to unintended security impacts.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2536873, 2536874, 2536875    
Bug Blocks:    

Description OSIDB Bzimport 2026-09-15 15:52:15 UTC 
Tornado before 6.5.8 contains an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by passing capitalized or legacy keyword arguments to set_cookie. Attackers can embed semicolon-delimited data in capitalized parameters like Domain, Path, or SameSite to bypass validation and modify cookie security attributes.