GHSA-hv2w-8mjj-jw22 MCP Java SDK has a Hardcoded Wildcard CORS (Access-Control-Allow-Origin: *)

• Maven io.modelcontextprotocol.sdk:mcp-core: >= 1.0.0, < 1.0.1 → fixed in 1.0.1 • Maven io.modelcontextprotocol.sdk:mcp-core: >= 1.1.0, < 1.1.1 → fixed in 1.1.1 • Maven io.modelcontextprotocol.sdk:mcp-core: < 0.18.3 → fixed in 0.18.3

Summary **Hardcoded Wildcard CORS (Access-Control-Allow-Origin: * )** • https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletSseServerTransportProvider.java#L289 • https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java#L525 Attack Scenario An attacker-controlled web page instructs the victim's browser to open GET https://internal-mcp-server/sse. Because Access-Control-Allow-Origin: * allows cross-origin SSE reads, the attacker's page receives the endpoint event — which contains the session ID. The attacker can then POST to that endpoint from their page using the victim's browser as a relay. Comparison with python-sdk No Access-Control-Allow-Origin header is emitted by either Python transport. The browser's default same-origin policy remains in full effect. https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/sse.py https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py Recommendation In the SDK, the transport layer should not own CORS policy. Server implementors who need cross-origin access can add a CORS filter at the servlet filter or Spring Security layer. Reference • https://cheatsheetseries.owasp.org/cheatsheets/HTTP_Headers_Cheat_Sheet.html#access-control-allow-origin