What is the CVSS score of CVE-2025-43859?

CVE-2025-43859 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.3%.

Which versions of Python are affected by CVE-2025-43859?

Organizations using h11 face critical risk from CVE-2025-43859 rated CVSS 9.1. Successful exploitation could critically impact the confidentiality, integrity, and availability of affected systems.. A patch is available.

Is there a public PoC exploit available for CVE-2025-43859?

Yes, a public proof-of-concept exploit is available for CVE-2025-43859. Prioritise patching immediately. EPSS: 0.3%.

How to fix or mitigate CVE-2025-43859?

Within 24 hours: Identify all affected systems and apply vendor patches immediately. Monitor vendor channels for patch availability.

Python CVE-2025-43859

CRITICAL

HTTP Request/Response Smuggling (CWE-444)

2025-04-24 security-advisories@github.com

Python Request Smuggling Information Disclosure Red Hat Suse

9.1

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

SUSE

CRITICAL

qualitative

Red Hat

7.4 HIGH

qualitative

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

Analysis Generated

Mar 28, 2026 - 18:38 vuln.today

CVE Published

Apr 24, 2025 - 19:15 nvd

CRITICAL 9.1

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

107,373 pypi packages depend on h11 (557 direct, 107,001 indirect)

Ecosystem-wide dependent count for version 0.16.0.

DescriptionGitHub Advisory

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

AnalysisAI

h11 is a Python implementation of HTTP/1.1. Rated critical severity (CVSS 9.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.

Technical ContextAI

This vulnerability is classified as HTTP Request/Response Smuggling (CWE-444), which allows attackers to manipulate HTTP request interpretation between frontend and backend servers. h11 is a Python implementation of HTTP/1.1. Prior to version 0.16.0, a leniency in h11's parsing of line terminators in chunked-coding message bodies can lead to request smuggling vulnerabilities under certain conditions. This issue has been patched in version 0.16.0. Since exploitation requires the combination of buggy h11 with a buggy (reverse) proxy, fixing either component is sufficient to mitigate this issue. Version information: version 0.16.0.

Affected ProductsAI

See vendor advisory for affected versions.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Enforce strict HTTP parsing, normalize requests at proxy layer, use HTTP/2 end-to-end, reject ambiguous headers.

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Vendor StatusVendor

SUSE

Severity: Critical

Product	Status
Container suse/sl-micro/6.0/baremetal-os-container:latest Container suse/sl-micro/6.0/base-os-container:latest Container suse/sl-micro/6.0/kvm-os-container:latest Container suse/sl-micro/6.0/rt-os-container:latest Container suse/sl-micro/6.0/toolbox:latest Image SL-Micro Image SL-Micro-Base Image SL-Micro-Base-RT Image SL-Micro-Base-RT-SelfInstall Image SL-Micro-Base-RT-encrypted Image SL-Micro-Base-SelfInstall Image SL-Micro-Base-encrypted Image SL-Micro-Base-qcow Image SL-Micro-Default Image SL-Micro-Default-SelfInstall Image SL-Micro-Default-encrypted Image SL-Micro-Default-qcow Image SLE-Micro Image SLE-Micro-BYOS Image SLE-Micro-BYOS-EC2 Image SLE-Micro-BYOS-GCE Image SLE-Micro-EC2 Image SLE-Micro-GCE	Affected
Image SL-Micro-Azure Image SL-Micro-BYOS-Azure Image SUSE-Multi-Linux-Manager-Proxy-BYOS-Azure Image SUSE-Multi-Linux-Manager-Server-Azure-llc Image SUSE-Multi-Linux-Manager-Server-Azure-ltd Image SUSE-Multi-Linux-Manager-Server-BYOS-Azure	Affected
SUSE Linux Enterprise Desktop 15 SP6 SUSE Linux Enterprise High Performance Computing 15 SP6 SUSE Linux Enterprise Module for Python 3 15 SP6 SUSE Linux Enterprise Server 15 SP6 SUSE Linux Enterprise Server for SAP Applications 15 SP6	Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS	Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS	Fixed

CVE-2025-43859 vulnerability details – vuln.today

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Python CVE-2025-43859

Severity by source

CVSS VectorGitHub Advisory

Lifecycle Timeline

Blast Radius

DescriptionGitHub Advisory

AnalysisAI

Technical ContextAI

Affected ProductsAI

RemediationAI

More in Python

Same weakness CWE-444 – HTTP Request/Response Smuggling

Same technique Request Smuggling

Vendor StatusVendor

SUSE

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External POC / Exploit Code