Description
h2 is a pure-Python implementation of a HTTP/2 protocol stack. Prior to version 4.3.0, an HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls. This issue has been patched in version 4.3.0.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| python-hyper | h2 | < 4.3.0 | — |
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 | 4.3.0-1 | — |
| Debian 13 | python-h2 | No fix yet | — |
| Debian 12 | python-h2 | No fix yet | — |
| Debian 11 | python-h2 | 4.0.0-3+deb11u1 | DLA-4290-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | python-h2 | No fix yet | — |
| Ubuntu 25.10 | 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 | 3.2.0-150200.3.5.1 | SUSE-SU-2025:03273-1 |
| SLES 15 SP6 | python-h2 | 3.2.0-150200.3.5.1 | SUSE-SU-2025:03273-1 |
| SLES 3 | python-h2 | 4.1.0-150400.8.6.1 | SUSE-SU-2025:03199-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | python-h2 | 4.2.0-160000.3.1 | SUSE-SU-2026:20187-1 |
| SLES 16.0 | python-h2 | 4.2.0-160000.3.1 | SUSE-SU-2026:20187-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | python-h2 | 4.3.0-1.1 | openSUSE-SU-2025:15496-1 |
| openSUSE Leap 16.0 | python-h2 | 4.2.0-160000.3.1 | openSUSE-SU-2026:20122-1 |
| openSUSE Leap 15.6 | python-h2 | 4.1.0-150400.8.6.1 | SUSE-SU-2025:03199-1 |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | python3-h2 | 4.0.0-2.amzn2023.0.4 | ALAS2023-2025-1181 |
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | airflow-3 +3 | 3.0.6-r0 | — |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| PyPI | h2 | < 4.3.0 | 4.3.0 | GHSA-847f-9342-265h |
Advisories 7
- openSUSE-SU-2026:20122-1 Security update for python-h2 SUSE / openSUSE Security Updates · Mar 23, 2026
- openSUSE-SU-2025:15496-1 python311-h2-4.3.0-1.1 on GA media SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:20187-1 Security update for python-h2 SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2025:03199-1 Security update for python-h2 SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2025:03273-1 Security update for python-h2 SUSE / openSUSE Security Updates · Mar 23, 2026
- DLA-4290-1 python-h2 - security update Debian Security (DSA / DLA) · Mar 9, 2026
- ALAS2023-2025-1181 Moderate: python-h2 security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Sep 15, 2025