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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-84380
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-02 18:21:29 UTC
Updated2026-09-02 19:18:08 UTC
DescriptionHTTPX2 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.

Risk And Classification

Primary CVSS: v3.1 5.6 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

Problem Types: CWE-444 | CWE-444 CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.6MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
3.1CNADECLARED5.6MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Pydantic Httpx2 affected < 2.11.0 Not specified

References

ReferenceSourceLinkTags
github.com/pydantic/httpx2/commit/829b93a2393212996f613e635261f777d9ec6eab [email protected] github.com
github.com/pydantic/httpx2/releases/tag/v2.11.0 [email protected] github.com
github.com/pydantic/httpx2/pull/1137 [email protected] github.com
github.com/pydantic/httpx2/security/advisories/GHSA-pf96-p4fj-6566 [email protected] github.com
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