# CVE-2025-43859: python3-h11: h11 is a Python implementation of HTTP/1.1

CVE-2025-43859 is fixed in 2 products on 1 platform, first by python3-h11 0.14.0-1ubuntu0.24.04.1, released April 24, 2025. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2025-43859
- Priority: High
- CVSS: 9.1 (Medium)
- EPSS: 0.0059
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 24, 2025

## Description

h11 is a Python implementation of HTTP/1.1. Prior to version 0.16.0, aleniency in h11's parsing of line terminators in chunked-coding messagebodies can lead to request smuggling vulnerabilities under certainconditions. This issue has been patched in version 0.16.0. Sinceexploitation requires the combination of buggy h11 with a buggy (reverse)proxy, fixing either component is sufficient to mitigate this issue.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | python-h11 Debian 12.15 (bookworm) | 0.14.0-1.1~deb12u1 | [DEBIAN-CVE-2025-43859](https://patchblox.com/security/data/fix/linux/debian-cve-2025-43859.md) | Apr 24, 2025 |
| Linux | python-h11 Debian 13.5 (trixie) | 0.14.0-1.1 | [DEBIAN-CVE-2025-43859](https://patchblox.com/security/data/fix/linux/debian-cve-2025-43859.md) | Apr 24, 2025 |
| Linux | python-h11 Debian 14 | 0.14.0-1.1 | [DEBIAN-CVE-2025-43859](https://patchblox.com/security/data/fix/linux/debian-cve-2025-43859.md) | Apr 24, 2025 |
| Linux | python-h11 opensuse-leap 15.6 | 0.14.0-150400.9.6.1 | [SUSE-SU-2025:1430-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1430-1.md) | May 2, 2025 |
| Linux | python-h11 sles 15.6 | 0.14.0-150400.9.6.1 | [SUSE-SU-2025:1430-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1430-1.md) | May 2, 2025 |
| Linux | python3-h11 Ubuntu 24.04.5 LTS (noble) | 0.14.0-1ubuntu0.24.04.1 | [python3-h11 0.14.0-1ubuntu0.24.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-python3-h11-0.14.0-1ubuntu0.24.04.1.md) | Apr 24, 2025 |
| Linux | python3-h11 Ubuntu 24.10 (oracular) | 0.14.0-1ubuntu0.24.10.1 | [python3-h11 0.14.0-1ubuntu0.24.10.1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-python3-h11-0.14.0-1ubuntu0.24.10.1.md) | Jan 16, 2026 |
| Linux | python3-h11 Ubuntu 25.04 (plucky) | 0.14.0-1ubuntu0.25.04.1 | [python3-h11 0.14.0-1ubuntu0.25.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-python3-h11-0.14.0-1ubuntu0.25.04.1.md) | Jan 16, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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