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CVE-2026-84378— HTTPX2: Quadratic SSE line buffering can cause CPU denial of service

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.

HTTPX2 是 Python 的下一代 HTTP 客户端。在 2.5.0 到 2.10.0 版本中， 中的 HTTPX2 服务器发送事件（Server-Sent Events, SSE）解析器在 中，当由攻击者控制或已被攻陷的 SSE 端点将一条未终止的行分割到多个响应块中时，会反复复制并重新扫描已缓冲的文本。该行为影响 和 ，总处理量随行长度呈平方级增长，使得精心构造的流可以消耗大量 CPU 并阻塞同步工作进程或异步事件循环。此问题已在 2.10.0 版本中修复。

CVSS 5.9 · Medium

Possible ATT&CK Techniques 1 AI

T1074 · Data Staged

Affected Version Matrix 1

VendorProduct Version RangeStatus
pydantic httpx2 >= 2.5.0, < 2.10.0 affected
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I. Basic Information for CVE-2026-84378

Vulnerability Information
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Vulnerability Title
HTTPX2: Quadratic SSE line buffering can cause CPU denial of service
Source: CVE Program / CVE List V5
Vulnerability Description
HTTPX2 is a next generation HTTP client for Python. From 2.5.0 until 2.10.0, the HTTPX2 Server-Sent Events parser in src/httpx2/httpx2/_sse.py repeatedly copies and rescans buffered text in _SSELineDecoder.decode() when an attacker-controlled or compromised SSE endpoint splits one unterminated line across many response chunks. The behavior affects httpx2.Client.sse() and httpx2.AsyncClient.sse(), and the total processing work grows quadratically with the line length, allowing a crafted stream to consume excessive CPU and block a synchronous worker or asynchronous event loop. This issue is fixed in version 2.10.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
pydantic httpx2 >= 2.5.0, < 2.10.0 -

II. Public POCs for CVE-2026-84378

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III. Intelligence Information for CVE-2026-84378

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Patches & Fixes for CVE-2026-84378 (2)

Vendor Pages for CVE-2026-84378 (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-2026-84380 5.6 MEDIUM HTTPX2: Conflicting Content-Length and Transfer-Encoding headers can be auto-generated
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-407

V. Comments for CVE-2026-84378

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