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

Quick assessment

Affected
python-hyper h11
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

h11是Nathaniel J. Smith个人开发者的一个用Python从头编写的小型HTTP/1.1库。 h11 0.16.0之前版本存在环境问题漏洞，该漏洞源于行终止符解析不当，可能导致请求夹带攻击。

CVSS 9.1 · Critical EPSS 0.59% · P48

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2025-43859

Vulnerability Information
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Vulnerability Title
h11 accepts some malformed Chunked-Encoding bodies
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5
Vulnerability Title
h11 环境问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
h11是Nathaniel J. Smith个人开发者的一个用Python从头编写的小型HTTP/1.1库。 h11 0.16.0之前版本存在环境问题漏洞，该漏洞源于行终止符解析不当，可能导致请求夹带攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Shenlong Deep Dive — AI Deep Analysis

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Affected Products

Vendor Product Affected Versions CPE Subscribe
python-hyper h11 < 0.16.0 -

II. Public POCs for CVE-2025-43859

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8244 chars
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III. Intelligence Information for CVE-2025-43859

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Patches & Fixes for CVE-2025-43859 (1)

Vendor Advisories for CVE-2025-43859 (1)

IV. Related Vulnerabilities

Same vendor: python-hyper
Same weakness: CWE-444