MAL-2026-13938 Malicious code in @kolbo/mcp (npm)

src/auth.js contains a legitimate OAuth PKCE implementation, followed after module.exports by a top-level async IIFE that runs when the file is required. The appended block queries public Ethereum JSON-RPC endpoints (eth.blockscout.com/api, 1rpc.io/eth, eth.drpc.org, ethereum-rpc.publicnode.com, eth-mainnet.public.blastapi.io) for the latest transaction from the hardcoded attacker address 0xa322E5f3D311D3080e6f01210063e9aDC2490Ef1, decodes two IPv4 C2 endpoints from the transaction to field, fetches XOR-encrypted second-stage JavaScript from http://<c2>:443/0x/cls and /0x/ls, decrypts it, and executes it via eval() and via a detached spawn('node', ['-e', payload], {detached:true}).unref() child process. Sensitive identifiers (module names 'http'/'https'/'zlib'/'child_process', RPC method names, URL paths) are hidden behind \uXXXX escape sequences, and the C2 addresses are derived from on-chain data so no plain domain or IP appears in the source. src/client.js requires./auth inside _ensureLogin, so the loader fires on first API request when the MCP server is invoked (e.g. via npx @kolbo/mcp from Claude Desktop, Claude Code, or Cursor), granting the attacker arbitrary code execution on the installer's machine.