CVE-2026-71554
h2: Duplicate Host header could facilitate request smuggling
MEDIUM 5.3EPSS 0.4%
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.
- Affected
- python-hyper · h2
- CVSS v3.1 GITHUB
- 5.3 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - EPSS
- 0.42% chance of exploitation in the next 30 days, 35th percentile
- Published
- 2026-08-06
- Updated
- 2026-08-08
Proof-of-concept exploits (1)
- SunandM/poc-h2-CVE-2026-715541★ · 2026-08-08