Vulnerability Report

CVE-2026-71554

Title: HTTP/2 Request Smuggling via multiple Host headers

Other

Proof Of Concept

PoC Available for CVE-2026-71554

CWE Category CWE-444
Published Date Aug 06, 2026
Modified Date Aug 08, 2026
Exploit Status Available
Score 5.3 CVSS v3.1
Exploit Probability (EPSS)
0.33%

Vulnerability Summary

CVE-2026-71554: 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.

Impacted Vendors

Analysis in Progress...

Reference Links

https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6 https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg
CVSS v3.1
Source Entity [email protected]
Severity MEDIUM
5.3
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2026-71554 Exploits & PoCs (Proof Of Concept)

GitHub https://github.com/SunandM/poc-h2-CVE-2026-71554
View Code
GitHub https://github.com/SunandM/poc-h2-duplicate-host
View Code
MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity LOW
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected Stack

No specific products linked.