Bug 2447144 (CVE-2026-1525)

Summary: CVE-2026-1525 undici: Undici: HTTP Request Smuggling and Denial of Service due to duplicate Content-Length headers
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: aazores, abarbaro, alizardo, anpicker, asoldano, bbaranow, bmaxwell, bparees, brian.stansberry, cmah, darran.lofthouse, dosoudil, dschmidt, eaguilar, ebaron, erezende, fjuma, hasun, istudens, ivassile, iweiss, jchui, jfula, jhe, jkoehler, jlanda, jolong, jowilson, kshier, ktsao, lphiri, mosmerov, msvehla, nboldt, nwallace, nyancey, ometelka, pberan, pesilva, pjindal, pmackay, psrna, ptisnovs, rstancel, sdawley, simaishi, smaestri, smcdonal, stcannon, syedriko, teagle, tom.jenkinson, xdharmai, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in undici, a Node.js HTTP/1.1 client. A remote attacker could exploit this vulnerability by sending HTTP/1.1 requests that include duplicate Content-Length headers with different casing (e.g., "Content-Length" and "content-length"). This can lead to HTTP Request Smuggling, a technique where an attacker sends an ambiguous request that is interpreted differently by a proxy and a backend server. Successful exploitation could result in unauthorized access, cache poisoning, or credential hijacking. It may also cause a Denial of Service (DoS) if strict HTTP parsers reject the malformed requests.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2447167, 2447168, 2447170, 2447174    
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Description OSIDB Bzimport 2026-03-12 21:01:56 UTC 
Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple conflicting Content-Length values on the wire.

Who is impacted:

  *  Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as flat arrays
  *  Applications that accept user-controlled header names without case-normalization


Potential consequences:

  *  Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request)
  *  HTTP Request Smuggling: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking