diff --git a/tools/webserver.js b/tools/webserver.js
index 7844464..b1db94a 100644
--- a/tools/webserver.js
+++ b/tools/webserver.js
@@ -6,6 +6,11 @@ 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);