python-hyper h11 up to 0.15.x request smuggling

Summaryinfo

A vulnerability was found in python-hyper h11 up to 0.15.x. It has been classified as critical. The impacted element is an unknown function. This manipulation causes request smuggling. This vulnerability is registered as CVE-2025-43859. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in python-hyper h11 up to 0.15.x. It has been declared as critical. Affected by this vulnerability is an unknown code block. The manipulation with an unknown input leads to a request smuggling vulnerability. The CWE definition for the vulnerability is CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2025-43859 since 04/17/2025. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available.

The vulnerability scanner Nessus provides a plugin with the ID 235092 (SUSE SLED15 / SLES15 / openSUSE 15 Security Update : python-h11 (SUSE-SU-2025:1430-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 0.16.0 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (235092) and CERT Bund (WID-SEC-2025-1022). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• Red Hat Ansible Automation Platform
• SUSE Linux
• IBM Business Automation Workflow
• Red Hat OpenStack

Productinfo

Type

• Programming Language Software

Vendor

• python-hyper

Name

• h11

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9
• 0.10
• 0.11
• 0.12
• 0.13
• 0.14
• 0.15

Website

• Product: https://github.com/python-hyper/h11/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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