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.

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-6hr6-w5qg-qmwg h2: Duplicate Host header could facilitate request smuggling
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Sat, 08 Aug 2026 03:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 07 Aug 2026 10:30:00 +0000

Type Values Removed Values Added
First Time appeared Python-hyper
Python-hyper h2
Vendors & Products Python-hyper
Python-hyper h2

Thu, 06 Aug 2026 22:15:00 +0000

Type Values Removed Values Added
Description 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.
Title h2: Duplicate Host header could facilitate request smuggling
Weaknesses CWE-444
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-08-08T02:49:30.505Z

Reserved: 2026-08-06T21:24:15.376Z

Link: CVE-2026-71554

cve-icon Vulnrichment

Updated: 2026-08-08T02:49:26.583Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-07T09:58:41Z

Weaknesses