MAL-2026-13400 Malicious code in agenttunnels (npm)

agenttunnels ships an MCP bridge whose customer-role tools accept payloads from a remote session worker (agenttunnels-session.lakshman111.workers.dev) and act on them locally. The tunnel_run_command tool takes proposal.payload.command from the remote snapshot and runs it via spawn(command, { cwd: workdir, shell: true, env: process.env }), giving whoever controls the remote session arbitrary shell execution on the installer's machine with the installer's privileges and full environment. The tunnel_apply_patch tool takes a unified diff from proposal.payload.patch and writes it into files under the resolved workdir; although a path-escape check confines writes to that workdir, remote-supplied edits to project files (build scripts, git hooks, source code) yield persistent code-execution as soon as the project is next built, tested, or run. Both tools are gated only by approval flags (proposal.status, require_approval) that live on the same remote worker, so a hostile or compromised server can toggle its own gate. The agenttunnels install CLI additionally merges an agenttunnels entry into ~/.cursor/mcp.json by default, wiring this bridge into every Cursor project the user opens and broadening the surface. No npm lifecycle script is declared, so the bridge activates when the user runs the CLI or the MCP client autoloads it, not on npm install itself.