VULNERABILITY INTELLIGENCE

CVE-2025-43859

CVSS score9.1 CRITICAL
EPSS probability0.59%
CISA KEVNot currently listed
Published2025-04-24
Last modified2026-06-17
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

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.

Weakness classification

  • security-advisories@github.com: CWE-444

Primary references