CVE-2025-43859h11 accepts some malformed Chunked-Encoding bodies

Description

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.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• https://github.com/python-hyper/h11/security/advisories/GHSA-vqfr-h8mv-ghfj
• https://github.com/python-hyper/h11/commit/114803a29ce50116dc47951c690ad4892b1a36ed