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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| python-hyper | h2 | < 4.4.1 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | python-h2 | No fix yet | — |
| Debian 13 | python-h2 | No fix yet | — |
| Debian 12 | python-h2 | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | python-h2 | No fix yet | — |
| Ubuntu 26.04 LTS | python-h2 | No fix yet | — |
| Ubuntu 24.04 LTS | python-h2 | No fix yet | — |
| Ubuntu 22.04 LTS | python-h2 | No fix yet | — |
| Ubuntu 20.04 LTS | python-h2 | No fix yet | — |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | python-h2 | No fix yet | — |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | python-h2 | 3.2.0-150200.3.8.1 | SUSE-SU-2026:3972-1 |
| SLES 3 | python-h2 | 4.1.0-150400.8.9.1 | SUSE-SU-2026:3970-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | python-h2 | 4.2.0-160000.4.1 | SUSE-SU-2026:23563-1 |
| SLES 16.0 | python-h2 | 4.2.0-160000.4.1 | SUSE-SU-2026:23563-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | python-h2 | 4.4.1-1.1 | openSUSE-SU-2026:11523-1 |
| openSUSE Leap 16.0 | python-h2 | 4.2.0-160000.4.1 | openSUSE-SU-2026:21693-1 |
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | airflow-3 | 3.3.1-r0 | — |
| Wolfi rolling | mitmproxy | 12.2.3-r5 | — |
| Wolfi rolling | open-webui | 0.11.0-r1 | — |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
GitHub 1 repository
-
SunandM/poc-h2-CVE-2026-71554 ★ 1 · Aug 7, 2026
PoC for CVE-2026-71554 - h2 duplicate Host header request smuggling primitive (fixed in 4.4.1)
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| PyPI | h2 | < 4.4.1 | 4.4.1 | GHSA-6hr6-w5qg-qmwg |
Advisories 5
- SUSE-SU-2026:23563-1 Security update for python-h2 SUSE / openSUSE Security Updates · Sep 29, 2026
- SUSE-SU-2026:3970-1 Security update for python-h2 SUSE / openSUSE Security Updates · Sep 13, 2026
- SUSE-SU-2026:3972-1 Security update for python-h2 SUSE / openSUSE Security Updates · Sep 13, 2026
- openSUSE-SU-2026:21693-1 Security update for python-h2 SUSE / openSUSE Security Updates · Aug 31, 2026
- openSUSE-SU-2026:11523-1 python313-h2-4.4.1-1.1 on GA media SUSE / openSUSE Security Updates · Aug 16, 2026