CVE-2026-71554
MEDIUMh2: Duplicate Host header could facilitate request smuggling
Title source: cnaExploitation Summary
EIP tracks 1 public exploit for CVE-2026-71554. PoCs published by SunandM.
AI-analyzed exploit summary This PoC demonstrates an HTTP request smuggling vulnerability in the h2 Python library (v4.4.0) due to improper handling of duplicate Host headers during HTTP/2 to HTTP/1.1 downgrade. The exploit shows how an attacker can bypass security checks and manipulate backend routing decisions.
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.
Exploits (1)
This PoC demonstrates an HTTP request smuggling vulnerability in the h2 Python library (v4.4.0) due to improper handling of duplicate Host headers during HTTP/2 to HTTP/1.1 downgrade. The exploit shows how an attacker can bypass security checks and manipulate backend routing decisions.
References (2)
Scores
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L