CVE-2025-43859

CRITICAL EPSS 40.4%
Published Apr 24, 20251y ago · Modified Jun 17, 20261w ago
9.1 CVSS 3.1
Critical
Find Similar
Published Apr 24, 2025 1y ago
Last Modified Jun 17, 2026 1w ago

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.

CVSS Details

Base Score
9.1
Exploitability
3.9
Impact
5.2
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality High
Integrity High
Availability None

Threat Intelligence

EPSS Exploit Probability
40.4% percentile
Exploit & Patch Status
No Known Exploit
No Patch Available

Weaknesses 1

CWE-444

References 2

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

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.