Tuesday, May 19, 2015

Cross-Site Request Forgery Detection with Burp and Regex

Cross-Site Request Forgery (CSRF) is an attack where a malicious person tries to force an authenticated user to execute some action. This attack can be caused by a GET or POST request where the server doesn’t validate the request is created by the correct authenticated user. To prevent CSRF, OWASP suggests using CSRF tokens by stating “The ideal solution is to only include the CSRF token in POST requests and have actions with state changing affect to only respond to POST requests. If sensitive server-side actions are guaranteed to only ever respond to POST requests, then there is no need to include the token in GET requests.” During web application penetration tests it is very common for only POST requests to modify state, so my goal is usually to find POST requests which execute a state-changing action and doesn’t have any CSRF protection such as a unique token. It’s very possible that even if CSRF protection is implemented, it’s done so incorrectly or in an incomplete manner. I thought of a nice little trick using Burp search and regular expressions (regex) which I think could be very useful in quickly determining if an application is potentially vulnerable.

Inefficient Detection

Burp Suite Proxy does have CSRF detection as an option in the active scanner engine, however I have found it to be inaccurate at times. Burp also has a ‘Generate CSRF PoC’ function which I do use after my regex search, however in a large application it isn’t realistic to manually look at all POST requests and generate a PoC for each one. A third option is Burp’s pro extension ‘CSRF Scanner’ which almost does what I need, as it lets me passively scan a branch in the site map for requests with a negative match on specific strings (such as unique token names). The biggest downside to this is it does not allow me to specify only a POST request, so I end up with a list of hundreds of requests in the Scanner Results tab.

Efficient Detection with Burp Search and Regex

Burp’s built-in Search is decent but lacking in a lot of areas. It doesn’t let users specify things like type of requests (GET, POST, etc.), ignore duplicate resources, multiple strings in one request, etc. However, Burp’s search does allow us to use regex which means a lot of this functionality we can do and it will help us detect potential CSRF.
Starting with a simple regex search to get an idea of how it works, we see an expression which matches an entire request/response pair:

So let’s create a regex which will help us find potential CSRF. We want a list of all POST requests which don’t have a unique token called ‘CSRF_Token’. To do this we use the regex ^POST((?!CSRF_Token).)*$

Excellent! We now have a comprehensive list of POST requests without a ‘CSRF_Token’ parameter. This will be sufficient for most applications. But what if there are multiple parameters or cookies used to protect against CSRF? Just make a simple modification to the regex and use ^POST((?!CSRF_Token|Cookie: CSRF_Cookie=).)*$. We can add as many keywords to do a negative match against as we want. Just add a pipe ‘|’ character followed by the keyword. To wrap this up here are some quick steps you can do to use this method:

  1. Map out an application by spidering as much of it as you can.
  2. Use Burp’s automated form submission spider option or manually submit forms throughout the application to get as many POST requests in your site map as possible.
  3. Figure out which CSRF defenses are being implemented. Usually I just see one POST parameter as a unique token but sometimes cookies, headers, viewstate, etc. are also used.
  4. Search your target from the sitemap:
  5. Select the regex checkbox and input your desired expression based on step 3. Here is an example format:
  6. Look at the list of requests to confirm they are candidates for CSRF. Find a request with a high impact (ex: Add an administrative user) and use Burp’s ‘Generate CSRF PoC’ function in Engagement tools.
  7. Open and submit the CSRF PoC as the authenticated victim and confirm if the action completed successfully.

Done! Hopefully this post helps you identify potential CSRF candidates. If you have any questions or comments please feel free to share.


Monday, February 2, 2015

Physical Home Security with Wireless IP Cameras and Monitoring Software

I see a lot of people who want a cheap and custom security system for their apartment, home, or business. I recently accomplished this and want to share how. Hopefully this will inspire people to be proactive in protecting their property.

Click here to view a PDF of this post

My security solution consists of:

Most of these things can be changed with alternatives such as the cameras, software, DNS host, online storage, etc. This was the setup which I found to work best for me.

So for about $240 total I have the following features:
  • Cameras for pictures and video recording capable of good quality night vision.
  • Motion detection to determine when to record video.
  • E-mail and text message alerts based off motion detection.
  • Remotely monitor the cameras from anywhere.
  • Online backup of all pictures and video in real time.

Step 1 - Configure Wireless IP Cameras

  • Plug in each camera to an outlet for power and connect it to your home network (router) with the provided ethernet cable.
  • Use the IP Camera Tool to find the IP address of the cameras. This tool can be found on the included CD or downloaded here: http://www.foscam.com/down4.aspx
  • Type the IP into your browser and connect over port 88, it will probably be something like
  • Login with the default 'admin' user and no password. You should then create a strong password for this account, with a max of 12 characters. I suggest using a password manager or similar to create a complex password. Once logged in you can go to Basic Settings>User Accounts to delete the 'admin' username and create your own.
  • Login to each camera and disable DHCP and assign each one its own static IP address. This makes it easy to unplug the camera when you don't need to use it and power it back on when you do.
  • Enter and save your network information in Network>Wireless Settings. This is assuming the cameras will be used wirelessly and not always connected via an ethernet cable.
That was easy! After you do this for each of your cameras you are pretty much done with setting them up. Go through each page and configure them how you like, but remember all motion detection and alarms will be done with the Blue Iris software (which is not a necessity, just my preference because of the many options). You could set up detection, alarms, and remote monitoring with just the Foscam cameras without Blue Iris software however there are drastically less configurable options.

Step 2 - Configure Blue Iris Software

At the time of writing this the current version of Blue Iris is It's still fairly new, with some people reporting bugs which is why I am waiting to update, plus my current setup works just fine. A very helpful resource is the help page and search which has pretty good documentation about the different features of Blue Iris. If you ever get stuck, use this:
  • Add a camera by clicking the '+' button in the top right corner of the Camera’s window.
  • Add the settings for the type of camera you own. There is a large drop down list to choose many different cameras. The user and password are the credentials you used to set up the cameras in step 1.
  • Now that the camera is added and connected to Blue Iris you can configure various motion detection and alarm options. Some of these options may take some trial and error to find which settings fit your desired security solution best.
  • These are my settings for motion detection and what actions are taken once motion is detected. I have it recording video and taking snapshots once any detection happens.
  • These are my alerts settings. I immediately get a text message and e-mail with snapshot if the motion detection is triggered.
At this point you have your cameras set up with the correct detection, recording, and alert settings. Currently recorded media is being saved to the local hard drive of the laptop or whatever device you are running Blue Iris on. The only thing left to do is online backup/storage just in case an intruder were to steal your laptop, thus losing all of the evidence, as well as accessing the cameras remotely (optional). I'm going to go over setting up Google Drive to automatically sync all of the recorded video and pictures since it's free and you get 15GB. Any good security solution should always have some type of online backup.

Step 3 - Create Online Backup

That's pretty much it! Test it out by dragging files into the folders to make sure they sync immediately. I like to have Google Drive boot on system startup so it's one less thing I have to do before I start Blue Iris.

Step 4 (Optional) - Configure Remote Access

Remote access consists of two things, the Blue Iris web server and a DNS host. Be aware this does increase the attack surface of your network so always use strong passwords and understand that nothing is ever completely secure. If you aren’t actively using your security system or planning on remotely accessing your cameras I would not run the Blue Iris web server unless you absolutely have to.
  • Go to Blue Iris options and select the Web Server tab. Use the 'Find address now' button or Google to find your public IP address. Choose a port number which is not being used on your laptop. I like to choose something not obvious (80, 443, etc.) however this is just an obfuscation technique and is not truly security. Add your local and external IP address as well.
  • Create a Blue Iris user and strong password which you can use to login remotely:
  • Login to your router and forward the port number you just configured for the web server: You should now be able to remotely access the Blue Iris login page from the external IP and port you configured previously. What if your public IP changes? Use dynamic DNS. There are many good free DNS options out there, I chose FreeDNS.
  • Create an account at FreeDNS, add a subdomain, and download a dynamic DNS client such as FreeDNS Update. Add your FreeDNS account information in the settings tab. You will want this running whenever you want to remotely access your cameras.

    You can now remotely access the Blue Iris login page remotely from your own domain on the port you configured in the Web Server tab:

Done! So before I leave the house I turn on the system by using the 'traffic signal' in Blue Iris and setting it to green. There is an option in Blue Iris to define the amount of time before motion detection and recording occurs. I have that option set to around 5 minutes so it doesn't start recording me leaving the house and send unnecessary sms and e-mail alerts. So before I leave my house I have my laptop running Blue Iris, Google Drive, and FreeDNS Update. I usually try to put the laptop in a place which isn't obvious so there is less chance of it being stolen if someone did break in. My laptop uses a Core i5-2410M CPU at 2.3GHz and usually runs around 10-30% load with everything running. Because of this you want to make sure your laptop is always plugged in and its power settings are configured to never sleep, hibernate, or shut down the hard drive.

I now have a custom security solution which was a fairly cheap investment. Please let me know if you have any questions, comments, or if this was helpful.