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

Quick assessment

Affected
pydantic httpx2
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Pydantic HTTPX2是Pydantic组织的一个支持HTTP/2协议的异步HTTP客户端库。 Pydantic HTTPX2 2.11.0之前版本存在输入验证错误漏洞，该漏洞源于src/HTTPX2/HTTPX2/_models.py文件中的Request._prepare()方法在处理默认请求头时将Content-Length和Transfer-Encoding头独立处理而非互斥，可能导致请求走私或连接去同步。

CVSS 5.6 · Medium EPSS 0.22% · P12

Possible ATT&CK Techniques 1 AI

T1597 · Search Closed Sources

Affected Version Matrix 1

VendorProduct Version RangeStatus
pydantic httpx2 < 2.11.0 affected
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I. Basic Information for CVE-2026-84380

Vulnerability Information
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Vulnerability Title
HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5
Vulnerability Title
Pydantic HTTPX2 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Pydantic HTTPX2是Pydantic组织的一个支持HTTP/2协议的异步HTTP客户端库。 Pydantic HTTPX2 2.11.0之前版本存在输入验证错误漏洞，该漏洞源于src/HTTPX2/HTTPX2/_models.py文件中的Request._prepare()方法在处理默认请求头时将Content-Length和Transfer-Encoding头独立处理而非互斥，可能导致请求走私或连接去同步。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
pydantic httpx2 < 2.11.0 -

II. Public POCs for CVE-2026-84380

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III. Intelligence Information for CVE-2026-84380

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Patches & Fixes for CVE-2026-84380 (3)

Vendor Advisories for CVE-2026-84380 (1)

Same Patch Batch · pydantic · 2026-09-02 · 5 CVEs total

CVE-2026-84381 8.1 HIGH HTTPX2: Secure WebSocket traffic sent without TLS through SOCKS proxies
CVE-2026-84382 7.5 HIGH HTTPX2: Streaming response decompression does not bound peak memory (decompression amplifi
CVE-2026-84378 5.9 MEDIUM HTTPX2: Quadratic SSE line buffering can cause CPU denial of service
CVE-2026-84379 5.3 MEDIUM HTTPX2: Multipart part header injection via unvalidated file Content-Type and custom heade

IV. Related Vulnerabilities

Same product: httpx2
Same vendor: pydantic
Same weakness: CWE-444

V. Comments for CVE-2026-84380

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