Node.JS static file web server. Put it in your path to fire up servers in any directory, takes an optional port argument.

static_server.js

var http = require("http"),
    url = require("url"),
    path = require("path"),
    fs = require("fs")
    port = process.argv[2] || 8888;

http.createServer(function(request, response) {

  var uri = url.parse(request.url).pathname
    , filename = path.join(process.cwd(), uri);
  
  path.exists(filename, function(exists) {
    if(!exists) {
      response.writeHead(404, {"Content-Type": "text/plain"});
      response.write("404 Not Found\n");
      response.end();
      return;
    }

    if (fs.statSync(filename).isDirectory()) filename += '/index.html';

    fs.readFile(filename, "binary", function(err, file) {
      if(err) {        
        response.writeHead(500, {"Content-Type": "text/plain"});
        response.write(err + "\n");
        response.end();
        return;
      }

      response.writeHead(200);
      response.write(file, "binary");
      response.end();
    });
  });
}).listen(parseInt(port, 10));

console.log("Static file server running at\n  => http://localhost:" + port + "/\nCTRL + C to shutdown");

I'm 15 years late to the party, but this is indeed insecure. PoC:
curl --path-as-is http://localhost:8888/../../../../../../../../etc/passwd

By default, when you send HTTP requests using curl, they'll be normalized. With --path-as-is flag you can prevent normalization, thus the exploit works. The same thing happens if you test the PoC in your browser. I think that's why most people didn't find the vulnerability.

This is insecure, someone can request /../../../etc/shadow or similar to read any file they want.

I guess you're not familiar with how path.join works, because as coded here it won't resolve to a directory outside of cwd directory branch.

No, I think you're not familiar with how path.join works, there is no mitigation for the directory boundary check here. We wrote a paper about this vulnerability as it spread almost EVERYWHERE.

You can test it in Node:
node -e 'console.log(path.join("/opt/app/www", "/../../../../etc/passwd")) // It will print /etc/passwd'