CVE-2025-43859

Published: Apr 24, 2025Modified: Jun 17, 2026Deferred

9.1

Vector

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

Exploitability: 3.9 / Impact: 5.2

Source: security-advisories@github.com (Secondary)

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.

Related CWEs

CWE-444

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

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.

References (2)

https://github.com/python-hyper/h11/commit/114803a29ce50116dc47951c690ad4892b1a36ed

Source: security-advisories@github.com

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

Source: security-advisories@github.com

Timeline

No history available yet.