CVE-2025-43859 | BDVDB-2026-276161 Detail

python-hyperh11

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.

Impact#

Per CVSS v3.1: confidentiality impact high, integrity impact high, availability impact none. Attack vector: network.

Weaknesses#

CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

References#

Exploit#

No public exploit known

History#

Version 12025-04-24Record published in the CVE List.

Published

Published: 2025-04-24
Last modified: 2025-04-24

Vendor information

Vendor: python-hyper
Product: h11

All python-hyper vulnerabilities

Score

9.1 Critical

EPSS

less than 1%, Very Low

Estimated chance of exploitation in the next 30 days. EPSS percentile: 48.7.

KEV

Not listed in the CISA Known Exploited Vulnerabilities catalog.

Impact

Not classified

Action

No specific action is recorded in the source data. Check the references for vendor guidance.

Affected Systems

Vulnerable
< 0.16.0
Fixed
Not stated

Scoring System

CVSS v4.0

Not available

CVSS v3.1

9.1 Critical

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

Metric breakdown
Attack Vector	Network
Attack Complexity	Low
Privileges Required	None
User Interaction	None
Scope	Unchanged
Confidentiality	High
Integrity	High
Availability	None

CVSS v3.0

Not available

CVSS v2

Not available

Source: CVE List v5 (record); CISA KEV (kev, action); FIRST EPSS (epss).