PyPi: H11

CVE-2025-43859

Safety vulnerability ID: 76903

This vulnerability was reviewed by experts

The information on this page was manually curated by our Cybersecurity Intelligence Team.

Created at Apr 24, 2025 Updated at Sep 20, 2025

Scan your Python projects for vulnerabilities →

Advisory

A leniency in h11's parsing of line terminators in chunked-coding message bodies can lead to request smuggling vulnerabilities under certain conditions.

Affected package

h11

Latest version: 0.16.0

A pure-Python, bring-your-own-I/O implementation of HTTP/1.1

Affected versions

Fixed versions

Vulnerability changelog

This vulnerability has no description

Resources

Use this package?

Scan your Python project for dependency vulnerabilities in two minutes

Scan your application

Severity Details

CVSS Base Score

CRITICAL 9.1

CVSS v3 Details

CRITICAL 9.1

Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): NONE
User Interaction (UI): NONE
Scope (S): UNCHANGED
Confidentiality Impact (C): HIGH
Integrity Impact (I): HIGH
Availability Availability (A): NONE