CVE catalog
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 th
- Severity
- Medium · CVSS 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - Published
- Source
- [NVD] · [CVE record]
- EPSS
- 0.42% · Oct 25, 2026
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.
Vulnerable and fixed packages
Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.
| Distribution | Package | Release | Version | Status |
|---|---|---|---|---|
| Debian | python-h2 | sid | 4.3.0-2 | vulnerable |
| Debian | python-h2 | forky | 4.3.0-2 | vulnerable |
| Debian | python-h2 | trixie | 4.2.0-1 | vulnerable |
| Debian | python-h2 | bookworm | 4.1.0-4 | vulnerable |
| Pip | h2 | Not reported | 4.4.1 | fixed |
| PyPI | h2 | Not reported | 4.4.1 | fixed |
| PyPI | h2 | Not reported | 4.4.1 | fixed |
| Suse | python-h2 | linux enterprise server 16.0 | 4.2.0-160000.4.1 | fixed |
| Suse | python-h2 | linux enterprise server for sap applications 16.0 | 4.2.0-160000.4.1 | fixed |
| Suse | python-h2 | linux enterprise module for server applications 15 sp7 | 3.2.0-150200.3.8.1 | fixed |
| Suse | python-h2 | linux enterprise module for python 3 15 sp7 | 4.1.0-150400.8.9.1 | fixed |
| Opensuse | python-h2 | leap 16.0 | 4.2.0-160000.4.1 | fixed |
| Opensuse | python-h2 | tumbleweed | 4.4.1-1.1 | fixed |
Fixed-version evidence
| Distribution | Package | Type | Release | Fixed version | Urgency | Origin | Bugs |
|---|---|---|---|---|---|---|---|
| Debian | python-h2 | source | sid | (unfixed) | not yet assigned | Not reported | [1143905] |
| Debian | python-h2 | source | forky | (unfixed) | not yet assigned | Not reported | [1143905] |
| Debian | python-h2 | source | trixie | (unfixed) | not yet assigned | Not reported | [1143905] |
| Debian | python-h2 | source | bookworm | (unfixed) | not yet assigned | Not reported | [1143905] |
| Pip | h2 | pip | Not reported | 4.4.1 | Not reported | Not reported | Not reported |
| PyPI | h2 | PyPI | Not reported | 4.4.1 | Not reported | PYSEC-2026-3628 | Not reported |
| PyPI | h2 | PyPI | Not reported | 4.4.1 | Not reported | GHSA-6HR6-W5QG-QMWG | Not reported |
| Suse | python-h2 | rpm | linux enterprise server 16.0 | 4.2.0-160000.4.1 | Not reported | SUSE-SU-2026:23563-1 | Not reported |
| Suse | python-h2 | rpm | linux enterprise server for sap applications 16.0 | 4.2.0-160000.4.1 | Not reported | SUSE-SU-2026:23563-1 | Not reported |
| Suse | python-h2 | rpm | linux enterprise module for server applications 15 sp7 | 3.2.0-150200.3.8.1 | Not reported | SUSE-SU-2026:3972-1 | Not reported |
| Suse | python-h2 | rpm | linux enterprise module for python 3 15 sp7 | 4.1.0-150400.8.9.1 | Not reported | SUSE-SU-2026:3970-1 | Not reported |
| Opensuse | python-h2 | rpm | leap 16.0 | 4.2.0-160000.4.1 | Not reported | OPENSUSE-SU-2026:21693-1 | Not reported |
| Opensuse | python-h2 | rpm | tumbleweed | 4.4.1-1.1 | Not reported | OPENSUSE-SU-2026:11523-1 | Not reported |
Notes
[trixie] python-h2: Minor issue [bookworm] python-h2: Minor issue
OpenFactory catalog packages
[Debian 12 (Bookworm)]
- [python3-h2]Affected
Source package: [python-h2]
Details (2)
4.1.0-4· all · bookwormAffected
nvd · python-h2 · debian · bookworm; nvd · python-h2 · debian · 12
4.1.0-4· all · bookwormAffected
nvd · python-h2 · debian · bookworm; nvd · python-h2 · debian · 12
[Debian 13 (Trixie)]
- [python3-h2]Affected
Source package: [python-h2]
Details (2)
4.2.0-1· all · trixieAffected
nvd · python-h2 · debian · 13
4.2.0-1· all · trixieAffected
nvd · python-h2 · debian · 13
[openSUSE Tumbleweed]
- [python313-h2]Unknown
Source package: [python-h2]
Details (1)
4.4.1-1.1· noarch · tumbleweedUnknown · Fixed:
4.4.1-1.1Version impact unknown
nvd · python-h2 · opensuse · tumbleweed
- [python314-h2]Unknown
Source package: [python-h2]
Details (1)
4.4.1-1.1· noarch · tumbleweedUnknown · Fixed:
4.4.1-1.1Version impact unknown
nvd · python-h2 · opensuse · tumbleweed
Observed:
References
- [https://ftp.suse.com/pub/projects/security/csaf/opensuse-su-2026_11523-1.json]
- [https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6]
- [https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg]
- [https://nvd.nist.gov/vuln/detail/CVE-2026-71554]
- [https://osv.dev/vulnerability/DEBIAN-CVE-2026-71554]
- [https://osv.dev/vulnerability/GHSA-6hr6-w5qg-qmwg]
- [https://osv.dev/vulnerability/SUSE-SU-2026:23563-1]
- [https://osv.dev/vulnerability/SUSE-SU-2026:3970-1]
- [https://osv.dev/vulnerability/SUSE-SU-2026:3972-1]
- [https://osv.dev/vulnerability/openSUSE-SU-2026:11523-1]
- [https://osv.dev/vulnerability/openSUSE-SU-2026:21693-1]
- [https://security-tracker.debian.org/tracker/CVE-2026-71554]
- [https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-71554.json]
[Debian Security Tracker] · [FIRST EPSS] · [GitHub Advisory Database] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX]