# CVE-2026-84380

## Summary

- **CVE ID:** CVE-2026-84380
- **Severity:** MEDIUM
- **CVSS Score:** 5.6 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L)
- **CWE:** CWE-444
- **Published:** Sep 2, 2026
- **Last Modified:** Sep 2, 2026

## 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.

## Affected Products

- pydantic — httpx2 (< 2.11.0)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.22%
- **EPSS Percentile:** 12.5

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._