Vulnerability · Published Sep 2, 2026 · Assigned by GitHub_M
CVE-2026-84380HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated
Medium 5.6
In plain English
A medium-severity security flaw in httpx2 from pydantic. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:14 | python-httpx2 | 2.12.0-1 | DEBIAN-CVE-2026-84380 |
| PyPI | httpx2 | 2.11.0 | GHSA-pf96-p4fj-6566 |
| PyPI | httpx2 | 2.11.0 | PYSEC-2026-3849 |
| Ubuntu:26.10 | python-httpx2 | no fix listed | UBUNTU-CVE-2026-84380 |
Affected products (as reported)
Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
References
- https://github.com/pydantic/httpx2/security/advisories/GHSA-pf96-p4fj-6566 x_refsource_CONFIRM
- https://github.com/pydantic/httpx2/pull/1137 x_refsource_MISC
- https://github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eab x_refsource_MISC
- https://github.com/pydantic/httpx2/releases/tag/v2.11.0 x_refsource_MISC