Official MCP Python SDK Flaw Can Let Malicious Servers Steal OAuth Credentials
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A malicious MCP server could trick an application built on the official MCP Python SDK into handing over the OAuth credentials it uses to authenticate to a legitimate service. The SDK maintainers detailed the issue in a security advisory.
According to the advisory, affected versions transmitted the client secret, the authorization code, and the PKCE proof key to a token endpoint controlled by the attacker. This means a hostile server could capture credentials intended for a genuine service and potentially use them to impersonate the client or gain unauthorized access.
Affected versions:
- MCP Python SDK releases prior to 1.30.0
The vulnerability is resolved in version 1.30.0. Users and developers running applications built on the SDK should upgrade to that version or later as soon as possible.
Given the nature of the flaw, operators should also review any OAuth clients that may have connected to untrusted or third-party MCP servers, and consider rotating client secrets and authorization codes that could have been exposed.
Source: The Hacker News
Has your organization already patched to MCP Python SDK 1.30.0, or are you reviewing your OAuth integrations for exposure?
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