AIKIDO-2026-156139

@modelcontextprotocol/sdk is vulnerable to Exposure of Sensitive Information to an Unauthorized Actor

Exposure of Sensitive Information to an Unauthorized ActorGHSA-6prh-2h8m-c8cw Published 6 days ago

Medium Risk

This Affects:

@modelcontextprotocol/sdk

0.0.1 - 1.31.0

Fixed in 1.32.0

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TL;DR

The SDK's HTTP client transports and OAuth client functions follow redirects to any origin, including cross origin destinations controlled by the server or authorization server being contacted. On a cross origin redirect, the new origin receives custom request headers such as an X-API-Key and the mcp-session-id header, and a 307 or 308 redirect also forwards the request body, including OAuth refresh_token and client_secret values. stdio clients are not affected; only StreamableHTTPClientTransport, SSEClientTransport, and the OAuth client functions such as auth() follow these redirects. The fix follows redirects only within the same origin, and does not follow them at all in browsers.

Who does this affect?

You are affected if you are using a version that falls within the vulnerable range and your application uses StreamableHTTPClientTransport, SSEClientTransport, or the SDK's OAuth client functions.