VULNERABILITY INTELLIGENCE

CVE-2026-71554

CVSS score5.3 MEDIUM
EPSS probability0.42%
CISA KEVNot currently listed
Published2026-08-06
Last modified2026-10-24
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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.

Weakness classification

  • security-advisories@github.com: CWE-444

Primary references