HTTPX2 is a next generation HTTP client for Python. Prior to 2.11.0, Request._prepare() in src/httpx2/httpx2/_models.py can add a body-derived Content-Length header to a request that already contains a caller-supplied Transfer-Encoding header because its setdefault() processing checks each default header independently rather than treating the two framing headers as mutually exclusive. Fixed-size byte, JSON, form, and known-length multipart bodies can therefore be serialized over HTTP/1.1 with both headers, allowing request smuggling or connection desynchronization when downstream intermediaries disagree about which framing header takes precedence. This issue is fixed in version 2.11.0.
History

Thu, 03 Sep 2026 16:00:00 +0000

Type Values Removed Values Added
First Time appeared Pydantic
Pydantic httpx2
Vendors & Products Pydantic
Pydantic httpx2

Thu, 03 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Moderate


Wed, 02 Sep 2026 21:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 02 Sep 2026 18:00:00 +0000

Type Values Removed Values Added
Description HTTPX2 is a next generation HTTP client for Python. Prior to 2.11.0, Request._prepare() in src/httpx2/httpx2/_models.py can add a body-derived Content-Length header to a request that already contains a caller-supplied Transfer-Encoding header because its setdefault() processing checks each default header independently rather than treating the two framing headers as mutually exclusive. Fixed-size byte, JSON, form, and known-length multipart bodies can therefore be serialized over HTTP/1.1 with both headers, allowing request smuggling or connection desynchronization when downstream intermediaries disagree about which framing header takes precedence. This issue is fixed in version 2.11.0.
Title HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated
Weaknesses CWE-444
References
Metrics cvssV3_1

{'score': 5.6, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-09-02T17:58:55.520Z

Updated: 2026-09-02T18:07:36.980Z

Reserved: 2026-09-01T16:27:58.130Z

Link: CVE-2026-84380

cve-icon Vulnrichment

Updated: 2026-09-02T18:07:32.081Z

cve-icon NVD

Status : Received

Published: 2026-09-02T18:21:29.513

Modified: 2026-09-02T19:18:08.113

Link: CVE-2026-84380

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-02T17:58:55Z

Links: CVE-2026-84380 - Bugzilla