CKAN MCP Server: Information disclosure via verbose error reflection

Summary

Error paths reflect raw upstream response bodies and internal exception messages back to the caller instead of a sanitized, generic message. When the server is pointed at (or redirected/SSRF'd to) a host that returns a non-CKAN response, or when an internal exception occurs, the caller receives verbatim upstream content and internal detail (hostnames, internal IPs, DB errors, stack fragments).

Affected code

src/utils/http.ts — the entire decoded upstream body is embedded in the thrown error, which formatCkanError returns to the tool result:

} else {
  throw new CkanApiError(
    `CKAN API returned success=false: ${JSON.stringify(decodedData)}`,   // full body reflected
    undefined,
    action
  );
}

src/worker.ts — the catch-all handler returns the raw Error.message in the JSON-RPC data field:

return new Response(JSON.stringify({
  jsonrpc: '2.0',
  error: { code: -32603, message: 'Internal error',
           data: error instanceof Error ? error.message : String(error) },  // raw internal message
  id: null
}), { status: 500, ... });

Impact

• Reflects arbitrary upstream response content to the caller. Combined with the SSRF vectors (advisories #01/#06), an attacker can use this as the read channel: point the server at an internal endpoint and receive its body inside the success=false error string (turning otherwise-blind SSRF into a semi-blind/return-value SSRF for any host that reaches the guards).
• Leaks internal operational detail via exception messages: node error codes and target addresses (e.g. ECONNREFUSED 169.254.169.254:80), which confirm internal reachability and infrastructure, and any stack/path fragments an upstream includes.
• Aids reconnaissance and error-oracle attacks against the deployment.

Severity is Low on its own (the server holds no credentials of its own and sends no auth upstream), but it meaningfully amplifies the SSRF findings by providing a response-content channel.

Proof of concept

poc/error-disclosure-poc.mjs reproduces both paths and shows an upstream body (containing a simulated DB error with an internal IP) and an internal ECONNREFUSED 169.254.169.254 message being reflected to the caller.

Remediation

• Return generic, action-scoped error messages to the caller; log the detailed upstream body/exception server-side only.
• Do not embed JSON.stringify(decodedData) in caller-visible errors; cap and redact any reflected content.
• In the Workers catch-all, omit error.message from the response data (or replace with a correlation id) in production.