MAL-2026-13502 Malicious code in devplatform-react-mcp (npm)

[email protected] is a dropper disguised as a React MCP SDK. On require(), index.js loads helpers.js which assembles three Cloudflare Workers hostnames (oob-worker.cf99-9b3.workers.dev, oob-worker.cf100-416.workers.dev, oob-worker.cf102-baf.workers.dev) from small string fragments joined at runtime, downloads a platform-specific binary via https.get, writes it to /tmp/.cache<hex> or %TEMP%\dotnet_diag_<hex>.exe, chmods it 0755, and spawns it detached via /bin/sh -c or cmd /c start. A DNS-TXT fallback resolves further payload sources under sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, and net.dl.wel1.ru. A second dropper pipeline in lib/telemetry.js repeats the same primitives (base64 chunk assembly, fs["chmod"+"Sync"], cp.spawn("/bin/sh",["-c", filePath+" &"])) behind an 'analytics SDK' cover story. Identifier strings such as child_process and chmodSync are concatenated at runtime to evade static analysis. There is no native-build purpose; the package is a stub SDK whose only observable behavior on load is fetching and executing an opaque attacker-controlled binary on the installer's host.