CVE-2026-77339

## Summary A malicious website can use DNS rebinding to control a developer's local process-compose MCP SSE listener when MCP SSE is enabled. The vulnerable path accepts browser-origin requests before any Host validation, Origin validation, or caller-secret check, then dispatches the requests into process-compose MCP tools. This advisory covers `https://github.com/F1bonacc1/process-compose`, confirmed at commit `d56aa59df04b72f8644811ac581a051bec05e485`. The issue is in the MCP SSE transport, not the Gin REST API. The REST API token middleware protects REST routes, but the MCP listener is started separately and does not inherit that protection. ## Affected Code Root cause: ```text src/types/mcp.go:24-30 SSE is the default MCP transport when mcp_server.transport is omitted. src/types/mcp.go:64-70 SSE configuration requires only host and port. There is no auth, Host allowlist, Origin allowlist, or caller-secret field. src/mcp/server.go:203-214 The server starts server.NewSSEServer(s.mcpServer) directly on the configured address. src/api/routes.go:32-39 X-PC-Token-Key middleware is installed on the Gin REST router, not on the MCP SSE listener. ``` Impact surface: ```text src/mcp/mcp_manager.go:33-38 expose_control_tools registers built-in process-compose control tools. src/mcp/control_tools.go:26-116 The registered tools start, stop, restart, scale, read logs, search logs, and truncate logs. src/mcp/control_tools.go:121-142 The registered tools return project and process state. ``` ## Reproduction Start process-compose from the affected commit with MCP SSE and built-in control tools enabled: ```bash workdir="$(mktemp -d)" cd "$workdir" git clone https://github.com/F1bonacc1/process-compose process-compose-target cd process-compose-target git checkout d56aa59df04b72f8644811ac581a051bec05e485 go build -o ./process-compose-poc . cat > process-compose-mcp-poc.yaml <<'YAML' mcp_server: host: 127.0.0.1 port: 8081 transport: sse expos