Unbounded request bodies expose MCP servers to unauthenticated denial-of-service attacks
Security advisories and vulnerability reports identify unbounded HTTP request-body handling across MCP SDKs, including the Java, TypeScript and Ruby SDKs. An unauthenticated attacker who can reach an affected HTTP endpoint may send an oversized or streamed request that exhausts server memory; patched versions are available, and a reverse proxy with a request-size limit can reduce exposure while systems are upgraded.
Bottom line — The Ruby SDK fix is in version 0.23.0; the Java advisory lists fixed releases 2.0.1, 1.1.4 and 0.18.4.
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The Java SDK advisory says the flaw affects Streamable HTTP, Stateless and SSE server transports when they are reachable without an upstream size limit.
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The Ruby advisory says the vulnerable transport reads and parses the full request body before session validation; version 0.23.0 contains the fix.
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A Ruby proof of concept reported memory use rising from 44 MB to 1.66 GB after one 512 MB request.
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The TypeScript vulnerability report also flags unrestricted JSON-RPC batch lengths, which can exhaust memory or starve the Node.js event loop.
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The Java advisory recommends enforcing request-body limits at a reverse proxy or gateway if an immediate upgrade is not possible.