Medium 5.6Published Sep 2, 2026

CVE-2026-84380HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated

Updated under an hour ago (2026-10-19 06:25 UTC)

Does this affect you?

It affects pydantic httpx2. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

Do this next

Start free and add your stack

Free account, 1 product

Every CVE for pydantic httpx2

Exploited in the last 30 days

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.

CVSS: 5.6 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
Weakness (CWE): CWE-444
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Awaiting Analysis
Record last updated: Sep 2, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

pydantic httpx2 pydantic:httpx2 (from the name)	before 2.11.0	CNA record

References

https://github.com/pydantic/httpx2/security/advisories/GHSA-pf96-p4fj-6566x-refsource-confirm
https://github.com/pydantic/httpx2/pull/1137x-refsource-misc
https://github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eabx-refsource-misc
https://github.com/pydantic/httpx2/releases/tag/v2.11.0x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.