fix: add DNS-level SSRF protection to MCP endpoints#2195
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fix: add DNS-level SSRF protection to MCP endpoints#2195
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The MCP health, tools, and client pool endpoints only validated URLs at the hostname string level (isValidUrl), allowing DNS rebinding attacks to reach internal services (e.g. cloud metadata at 169.254.169.254). Add a shared ssrfSafeFetch wrapper using undici with a custom DNS lookup callback that validates resolved IPs at connection time, matching the existing protection in fetch-url. Apply it to all MCP SDK transport instantiations.
Replace the inline undici Agent in fetch-url with the shared ssrfSafeFetch wrapper from urlSafety.ts, removing ~30 lines of duplicated DNS lookup validation code.
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Summary
isValidUrl(), which doesn't catch DNS rebinding attacks (e.g. a domain resolving to169.254.169.254for cloud metadata theft)ssrfSafeFetchwrapper inurlSafety.tsusing undici with a custom DNS lookup callback that validates resolved IPs at connection time — same pattern already used byfetch-urlStreamableHTTPClientTransportandSSEClientTransport) across health, tools, and clientPoolReported via HackerOne #31963.