Server-Side Request Forgery in mcp-remote

Executive Summary

This is a Server-Side Request Forgery (SSRF) vulnerability affecting mcp-remote versions 0.1.32 through 0.1.38. It occurs when the client extracts a resource_metadata URL from a remote MCP server's WWW-Authenticate header and fetches it without proper validation. This allows an attacker to force the client to send HTTP requests to unintended targets like localhost services, private network addresses, or cloud metadata endpoints.

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Detection Guidance

To detect this SSRF vulnerability, check if you are running mcp-remote versions 0.1.32 through 0.1.38. Run: mcp-remote --version. Inspect network traffic for unexpected outbound requests to localhost, private IPs, or cloud metadata endpoints. Use tools like tcpdump or Wireshark to monitor HTTP requests originating from the mcp-remote process.

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Impact Analysis

An attacker could exploit this to access internal services on your machine, exfiltrate sensitive data from local services, or interact with cloud provider metadata endpoints to obtain credentials or other sensitive information. This could lead to unauthorized access, data breaches, or further compromise of your system.

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Compliance Impact

This vulnerability could lead to unauthorized data access or exfiltration, violating GDPR's data protection requirements or HIPAA's safeguards for protected health information. Organizations may face compliance violations, legal penalties, and reputational damage if exploited.

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Mitigation Strategies

Immediately upgrade mcp-remote to a patched version beyond 0.1.38. If upgrading is not possible, apply an outbound-destination policy to restrict allowed schemes, reject loopback, private, and reserved addresses. Ensure all OAuth discovery requests enforce origin binding and validate URLs strictly before processing.

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