CVE-2025-43859

EUVD-2025-11981

24.04.2025, 19:15

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.

HTTP Request/Response Smuggling

Provider	Type	Base Score	Atk. Vector	Atk. Complexity	Priv. Required	Vector
NIST	Primary	9.1 CRITICAL	NETWORK	LOW	NONE	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Awaiting analysis

This vulnerability is currently awaiting analysis.

Base Score

CVSS 3.x

EPSS Score

Percentile: 45.52%

Debian Releases

Debian Product

Codename

python-h11

bookworm	0.14.0-1.1~deb12u1 fixed
bullseye	0.12.0-1 fixed
forky	0.16.0-2 fixed
sid	0.16.0-2 fixed
trixie	0.14.0-1.1 fixed

Ubuntu Releases

Ubuntu Product

Codename

python-h11

focal	not-affected
jammy	not-affected
noble	Fixed 0.14.0-1ubuntu0.24.04.1 released
oracular	Fixed 0.14.0-1ubuntu0.24.10.1 released
plucky	Fixed 0.14.0-1ubuntu0.25.04.1 released

Common Weakness Enumeration

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

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

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