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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.

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 2.5.0版本至2.10.0之前版本存在资源管理错误漏洞，该漏洞源于src/httpx2/httpx2/_sse.py中的_SSELineDecoder.decode()函数反复复制和重新扫描缓冲文本，导致处理工作量随行长度二次增长，可能允许攻击者通过特制流消耗过多CPU并阻塞同步工作线程或异步事件循环。

CVSS 5.9 · Medium EPSS 0.32% · P23

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
Vulnerability Title
Pydantic HTTPX2 资源管理错误漏洞
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 2.5.0版本至2.10.0之前版本存在资源管理错误漏洞，该漏洞源于src/httpx2/httpx2/_sse.py中的_SSELineDecoder.decode()函数反复复制和重新扫描缓冲文本，导致处理工作量随行长度二次增长，可能允许攻击者通过特制流消耗过多CPU并阻塞同步工作线程或异步事件循环。
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 >= 2.5.0, < 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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