CVE-2026-71554
h2: Duplicate Host header could facilitate request smuggling
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.
INFO
Published Date :
Aug. 6, 2026, 10:18 p.m.
Last Modified :
Aug. 6, 2026, 10:18 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-71554
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update the h2 library to version 4.4.1 or later.
- Ensure consuming applications handle Host headers correctly.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-71554.
| URL | Resource |
|---|---|
| https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6 | |
| https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-71554 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-71554
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-71554 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-71554 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Aug. 06, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'python-hyper', 'product': 'h2', 'versions': [{'status': 'affected', 'version': '< 4.4.1'}]}] 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Added CWE CWE-444 Added Reference https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6 Added Reference https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg