CVE-2026-59950

Analyzed Analyzed - Analysis Complete

MCP Python SDK WebSocket Origin Validation Bypass

Publication date: 2026-07-15

Last updated on: 2026-07-17

Assigner: GitHub, Inc.

Description

The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.28.1, the deprecated mcp.server.websocket.websocket_server transport accepted WebSocket handshakes without applying Host or Origin header validation, leaving no SDK-level way to restrict which origins could connect to applications that exposed that transport. This issue is fixed in version 1.28.1.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-07-15

Last Modified

2026-07-17

Generated

2026-08-05

AI Q&A

2026-07-16

EPSS Evaluated

2026-08-03

NVD

CVE-2026-59950

Affected Vendors & Products

Vendor	Product	Version / Range
lfprojects	mcp_python_sdk	to 1.28.1 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-346	The product does not properly verify that the source of data or communication is valid.
CWE-1385	The product uses a WebSocket, but it does not properly verify that the source of data or communication is valid.

Attack-Flow Graph

Executive Summary

The MCP Python SDK before version 1.28.1 has a vulnerability in its deprecated WebSocket transport (mcp.server.websocket.websocket_server). It fails to validate Host or Origin headers during WebSocket handshakes, allowing any origin to connect to applications using this transport. This could enable unauthorized access or interactions with the SDK.

Detection Guidance

The vulnerability involves the MCP Python SDK's WebSocket transport not validating Host or Origin headers. To detect it, check if any applications using mcp versions before 1.28.1 expose the deprecated websocket_server transport. Inspect network traffic for unvalidated WebSocket connections to this transport.

Impact Analysis

This vulnerability could allow attackers to connect to your MCP Python SDK application via WebSocket without proper origin restrictions. This may lead to unauthorized data access, manipulation, or disruption of services if the application processes untrusted input.

Compliance Impact

This vulnerability could violate compliance requirements that mandate strict access controls and data protection, such as GDPR's principle of data protection by design or HIPAA's access controls. Unauthorized connections may lead to data breaches or unauthorized processing.

Mitigation Strategies

Upgrade the MCP Python SDK to version 1.28.1 or later to apply Host and Origin header validation. If upgrading is not possible, disable the deprecated websocket_server transport in affected applications to prevent unauthorized WebSocket connections.

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