Bug 2528756 (CVE-2026-84933)

Summary: CVE-2026-84933 undici: undici: Cross-user cookie disclosure via Set-Cookie caching
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: abarbaro, akhatavk, alizardo, aos-team-art-private, asdas, ataylor, cdrage, dbruscin, dpaolell, dschmidt, eborisov, ehugonne, gbenhaim, gtanzill, jbuscemi, jchui, jdelft, jhe, jlanda, jupierce, kshier, ktsao, kvanderr, lball, lchilton, lgarciaa, mbiarnes, mstipich, nboldt, ngough, niyer, oaljalju, ppalepu, ppostler, prdhamdh, psrna, rexwhite, rhel-process-autobot, rushinde, sdawley, sfeifer, sghai, sidsharm, simaishi, stcannon, sthirugn, suppawar, teagle, twaugh, veshanka, vlaad, watson-tool-maintainers, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in undici. The software's caching mechanism, when operating in shared cache mode, improperly stores responses that include 'Set-Cookie' headers. This oversight allows an untrusted server to inject cookies into cached responses. Consequently, sensitive cookie information from one user can be inadvertently disclosed to another user accessing the same cached content.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2531876    
Bug Blocks:    

Description OSIDB Bzimport 2026-09-04 17:19:49 UTC 
undici's cache interceptor does not handle the Set-Cookie response header anywhere in its cache path, so it neither refuses to store nor strips that header. In shared cache mode, which is the default, an otherwise cacheable response that carries a Set-Cookie header, for example one marked with a public and max-age directive, is stored and then re-served to a later caller that matches the same cache key. As a result one caller's cookie is disclosed to a different caller, and an untrusted server can inject cookies into cached responses served to all subsequent callers. This violates the requirement that a shared cache must not store cookies. This affects undici versions from 7.0.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.