Web Application Exploits and Defenses (Part 1)

A Codelab by Bruce Leban, Mugdha Bendre, and Parisa Tabriz

Table of Contents


To access Gruyere, go to http://google-gruyere.appspot.com/start. AppEngine will start a new instance of Gruyere for you, assign it a unique id and redirect you to http://google-gruyere.appspot.com/123/ (where 123 is your unique id). Each instance of Gruyere is "sandboxed" from the other instances so your instance won't be affected by anyone else using Gruyere. You'll need to use your unique id instead of 123 in all the examples. If you want to share your instance of Gruyere with someone else (e.g., to show them a successful attack), just share the full URL with them including your unique id.

The Gruyere source code is available online so that you can use it for white-box hacking. You can browse the source code at http://google-gruyere.appspot.com/code/ or download all the files from http://google-gruyere.appspot.com/gruyere-code.zip. If want to debug it or actually try fixing the bugs, you can download it and run it locally. You do not need to run Gruyere locally in order to do the lab.

Running locally

Reset Button

As noted above, each instance is sandboxed so it can't consume infinite resources and it can't interfere with anyone else's instance. Notwithstanding that, it is possible to put your Gruyere instance into a state where it is completely unusable. If that happens, you can push a magic "reset button" to wipe out all the data in your instance and start from scratch. To do this, visit this URL with your instance id:

About the Code

Gruyere is small and compact. Here is a quick rundown of the application code:

Features and Technologies

Gruyere includes a number of special features and technologies which add attack surface. We'll highlight them here so you'll be aware of them as you try to attack it. Each of these introduces new vulnerabilities.

Using Gruyere

To familiarize yourself with the features of Gruyere, complete the following tasks:

This covers the basic features provided by Gruyere. Now let's break them!

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The code portions of this codelab are licensed under the Creative Commons Attribution-No Derivative Works 3.0 United States license <http://creativecommons.org/licenses/by-nd/3.0/us>. Brief excerpts of the code may be used for educational or instructional purposes provided this notice is kept intact. Except as otherwise noted the remainder of this codelab is licensed under the Creative Commons Attribution 3.0 United States license <http://creativecommons.org/licenses/by/3.0/us>.