Model Context Protocol Python SDK up to 1.29.0/2.0.1 Streamable HTTP Session Manager resource consumption

Summaryinfo

A vulnerability described as problematic has been identified in Model Context Protocol Python SDK up to 1.29.0/2.0.1. This impacts an unknown function of the component Streamable HTTP Session Manager/SSE Message Endpoint/OAuth Authorization Server Routes. The manipulation results in resource consumption. This vulnerability is cataloged as CVE-2026-109527. The attack may be launched remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as problematic has been found in Model Context Protocol Python SDK up to 1.29.0/2.0.1. Affected is an unknown code block of the component Streamable HTTP Session Manager/SSE Message Endpoint/OAuth Authorization Server Routes. The manipulation with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-109527 since 10/12/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 1.29.1 or 2.1.0 eliminates this vulnerability.

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Productinfo

Type

• Programming Language Software

Vendor

• Model Context Protocol

Name

• Python SDK

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11
• 1.12
• 1.13
• 1.14
• 1.15
• 1.16
• 1.17
• 1.18
• 1.19
• 1.20
• 1.21
• 1.22
• 1.23
• 1.24
• 1.25
• 1.26
• 1.27
• 1.28
• 1.29.0
• 2.0.0
• 2.0.1

License

• open-source

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CPE 2.2info

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