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MCP Python SDK OAuth flaw allows credential theft

By PulseAugur Editorial · [1 sources] ·

A security vulnerability has been identified in the MCP Python SDK, affecting versions 1.9.1–1.29.1 and 2.0.0–2.1.1. The flaw allows a malicious MCP server to intercept an application's OAuth credentials, including client secrets and authorization codes, by misdirecting the client to an attacker-controlled token endpoint. This could lead to unauthorized access to the application's full permissions. Remediation involves upgrading the SDK, explicitly providing the issuer URL for OAuth providers, and rotating compromised secrets. AI

IMPACT Potential for credential theft in applications using the MCP Python SDK, impacting security and data integrity.

RANK_REASON Security advisory detailing a vulnerability in a specific software library.

Read on dev.to — MCP tag →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

MCP Python SDK OAuth flaw allows credential theft

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COVERAGE [1]

  1. dev.to — MCP tag TIER_1 English(EN) · ScriptMasterLabs ·

    What Is the MCP Python SDK OAuth Flaw? (Sept 29, 2026)

    <p>Today's security advisory on the official MCP Python SDK is worth more than a skim: a malicious MCP server could steal an app's OAuth credentials — client secret, authorization code, and the PKCE proof key — by answering one question wrong: "where do I log in?"</p> <p><strong>…

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