Bug 2528783 (CVE-2026-18540)

Summary: CVE-2026-18540 undici: undici: HTTP response splitting via retry interceptor
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
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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A flaw was found in undici. An attacker-controlled upstream server can exploit a vulnerability in the retry interceptor, which incorrectly appends data to a ranged retry response. This can cause the response body to be longer than the Content-Length observed by the application. Consequently, an application relaying such a response to a downstream HTTP/1.1 peer without proper framing normalization may enable HTTP response splitting or desynchronization, allowing an attacker to inject arbitrary content into subsequent responses.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2531718, 2531719, 2531720, 2531721    
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Description OSIDB Bzimport 2026-09-04 17:33:10 UTC 
undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server delivers part of a body without a trustworthy resume checkpoint, for example a non-success response whose headers were already sent or a partial-content response with an unusable content range, then closes the connection and answers the resumed range request with more bytes. As a result the response body can be longer than the Content-Length that the application observes. An application that relays such a response to a downstream HTTP/1.1 peer without normalizing the framing can emit a body that exceeds the forwarded Content-Length, and the excess bytes can be interpreted as the start of a following response, which enables downstream response splitting or desynchronization. Exploitation requires an attacker-controlled upstream server and an application that forwards the response through a framing-sensitive path. This affects undici versions before 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.