diff --git a/app.js b/app.js
index dcc3798..535dce7 100644
--- a/app.js
+++ b/app.js
@@ -5,6 +5,11 @@ var http = require("http"),
     port = process.argv[2] || 8888;
 
 http.createServer(function(request, response) {
+    if (path.normalize(decodeURI(request.url)) !== decodeURI(request.url)) {
+        response.statusCode = 403;
+        response.end();
+        return;
+    }
 
   var uri = url.parse(request.url).pathname
     , filename = path.join(process.cwd(), uri);