Bug 2512214 (CVE-2026-71554)

Summary: CVE-2026-71554 h2: h2: Request smuggling due to duplicate Host headers
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: dschmidt, dymurray, eglynn, ibolton, ikhan, jjoyce, jlanda, jmatthew, jmontleo, jpretori, jschluet, kaycoth, kshier, lhh, mburns, mgarciac, pgaikwad, rbobbitt, rjohnson, simaishi, slucidi, sseago, stcannon, teagle, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in h2, a Python library for HTTP/2. This vulnerability allows a remote attacker to perform request smuggling. The library incorrectly processes HTTP/2 requests that contain more than one Host header. When these requests are downgraded to HTTP/1.1 by a consuming application, the duplicate Host headers can be exploited to bypass security mechanisms and potentially gain unauthorized access or manipulate data.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Description OSIDB Bzimport 2026-08-06 22:22:37 UTC 
h2 is a pure-Python implementation of a HTTP/2 protocol stack. Versions up to and including 4.4.0 accept request header blocks containing more than one Host header, and forward every Host header to the consuming application. Where the consumer downgrades HTTP/2 to HTTP/1.1, the resulting request carries two Host header lines, providing a request smuggling primitive. This issue is fixed in version 4.4.1.