CVE-2026-84380

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.

• CWE-444

• https://github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eab
• https://github.com/pydantic/httpx2/pull/1137
• https://github.com/pydantic/httpx2/releases/tag/v2.11.0
• https://github.com/pydantic/httpx2/security/advisories/GHSA-pf96-p4fj-6566

Published

Sep 2, 2026

Last Modified

Sep 9, 2026

Status

Awaiting Analysis

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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