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CVE-2026-109527— Model Context Protocol Python SDK HTTP and OAuth endpoints allow memory exhaustion through unbounded request bodies

Quick assessment

Affected
modelcontextprotocol python-sdk
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.

Model Context Protocol（MCP）Python SDK 是用于 MCP 服务器和客户端的官方 Python SDK。在 mcp 版本低于 1.29.1 以及 2.0.0a1 至 2.0.1 版本中，Streamable HTTP 会话管理器、SSE 消息端点以及 OAuth 授权服务器路由均未对 HTTP 请求体的大小实施最大限制，而是将完整的请求体缓冲至内存中。能够访问受影响端点的未认证远程客户端可以发送一个声明体积巨大或通过流式方式传输的请求体，从而在进程内存中占用远超请求体实际大小的内存空

CVSS 7.5 · High EPSS 0.70% · P52

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
modelcontextprotocol python-sdk < 1.29.1 affected
>= 2.0.0a1, < 2.1.0 affected
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I. Basic Information for CVE-2026-109527

Vulnerability Information
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Vulnerability Title
Model Context Protocol Python SDK HTTP and OAuth endpoints allow memory exhaustion through unbounded request bodies
Source: CVE Program / CVE List V5
Vulnerability Description
The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. In mcp versions before 1.29.1 and from 2.0.0a1 through 2.0.1, the Streamable HTTP session manager, SSE message endpoint, and OAuth authorization-server routes buffer complete HTTP request bodies without enforcing a maximum size. An unauthenticated remote client able to reach an affected endpoint can send a large declared or streamed request body that consumes multiple times the body size in process memory and can repeatedly exhaust memory or terminate the server. Stdio-only servers and deployments with an effective upstream request-size limit are not affected, and applications that use StreamableHTTPServerTransport directly remain responsible for enforcing their own limit. The standard SDK server applications and session managers are fixed in versions 1.29.1 and 2.1.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
modelcontextprotocol python-sdk < 1.29.1 -

II. Public POCs for CVE-2026-109527

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III. Intelligence Information for CVE-2026-109527

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Patches & Fixes for CVE-2026-109527 (1)

Other References for CVE-2026-109527 (3)

Same Patch Batch · modelcontextprotocol · 2026-10-14 · 3 CVEs total

CVE-2026-108395 7.5 HIGH Model Context Protocol Java SDK HTTP server transports allow memory exhaustion through unb
CVE-2026-59951 6.9 MEDIUM MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resourc

IV. Related Vulnerabilities

Same product: python-sdk
Same vendor: modelcontextprotocol
Same weakness: CWE-770

V. Comments for CVE-2026-109527

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