---
id: CVE-2026-84380
title: HTTPX2 is a next generation HTTP client for Python
summary: >-
  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 h…
severity: medium
cvss: 5.6
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L'
cwe:
  - CWE-444
vendor: httpx2
product: httpx2
affected:
  - httpx2 < 2.11.0
patched:
  - httpx2 2.11.0
published: '2026-09-02'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T21:05:23.237'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-84380'
references:
  - url: >-
      https://github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eab
    label: security-advisories@github.com
  - url: 'https://github.com/pydantic/httpx2/pull/1137'
    label: security-advisories@github.com
  - url: 'https://github.com/pydantic/httpx2/releases/tag/v2.11.0'
    label: security-advisories@github.com
  - url: 'https://github.com/pydantic/httpx2/security/advisories/GHSA-pf96-p4fj-6566'
    label: security-advisories@github.com
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-84380'
  - url: 'https://github.com/pydantic/httpx2'
  - url: 'https://github.com/advisories/GHSA-pf96-p4fj-6566'
  - url: 'https://pypi.org/project/httpx2'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-84380.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-84380'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2527695'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-84380'
tags:
  - nvd
  - osv
  - pip
  - ghsa
  - csaf
  - vex
  - red-hat
epss: 0.00356
epssPercentile: 0.2659
aliases:
  - GHSA-pf96-p4fj-6566
  - PYSEC-2026-3849
ecosystem: pip
ingestedAt: '2026-09-08T21:11:12.322Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-84380)

Affected packages:

- `httpx2 < 2.11.0`

Patched in:

- `httpx2 2.11.0`

Source: https://osv.dev/vulnerability/GHSA-pf96-p4fj-6566

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Lightspeed Core, Red Hat OpenShift AI (RHOAI) · no fix planned: Lightspeed Core, Red Hat OpenShift AI (RHOAI) · updated 2026-09-22 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-84380.json)