Sunday, August 17, 2014

Scan the Internet & Screenshot All the Things

During Defcon 22, @ErrataRob, @paulm and @Viss (mass)scanned the Internet and presented some Tips, Tricks and Results. Lots of people confronted @Viss after he posted some VNC screenshots on his Twitter timeline. He posted a follow-up article on his blog and Kashmir Hill, from Forbes, wrote an article about the exposed VNC services.

Internet scanning isn't new anymore and people are still surprised with these results. For this post, I'll share some techniques I commonly use to map and screenshot several Internet services during pentest engagements. All this could easily be adapted for other protocols and services, so let's start to Screenshot All the Things.



VNC

The easiest way to snapshot these services is to use preexisting tools and script/mod them according to your needs. In order to take screenshots from VNC, I generally use noVNC (an HTML5 VNC client) and a command line utility to capture the WebKit's rendering of a web page.

The process is pretty straightforward:

1 - Clone the noVNC project from github:

git clone git://github.com/kanaka/noVNC

2 - Start the mini-webserver and specify the location of the VNC server you want to screenshot:

./noVNC/utils/launch.sh --vnc 192.168.1.142:5900


3 - Take a webpage screenshot from command line using CutyCapt, for example:

cutycapt --url="http://127.0.0.1:6080/vnc_auto.html" --javascript=on --out=vnc.png --delay=3000


4 - Profit!!!

Now all you have to do is masscan the target for ports 5900-5910 (used by VNC), save the results on a text file and create a simple script to take the screenshots. You can also try vncsnapshot, used by @paulm during his Toorcon 2013 talk.

RDP

My tool of choice for taking snapshots of RDP services is Spark View. There's an HTML5 version for the tool available here and the process is quite similar to the VNC one:

1 - Download and install Spark View for Windows or Linux. Follow the procedure from the Admin Manual, install J2SE JDK, set the JAVA_HOME environment variable, extract, configure and compile the utils from commons-daemon-native.tar.gz. On Debian derivatives, you may need to edit SparkGateway.sh and change the source function library to "/lib/lsb/init-functions".

2 - Start the service (./SparkGateway.sh start) and test it by accessing your local IP on port 80. Remote Spark provides a live demo for their solution here.


3 - Specify the RDP server settings on the querystring and take a webpage screenshot using a command line tool. I'm going to use phantomjs + url-to-image.js for this example:

phantomjs url-to-image.js "http://127.0.0.1/rdpdirect.html?gateway=127.0.0.1&server=192.168.1.189&width=800&height=600&color=16" rdp.png 800 600


4 - Profit!!!

Some commercial tools like Nessus also connects to RDP services and captures screenshots. Taking screenshots from RDP services is very useful to fingerprint operating systems and to map/identify domains and users on the network. I always output these images to OCR tools like tesseract and gocr in order to generate wordlists and compile other useful data:

RDP screenshot
gocr output
tesseract output

HTTP

There's nothing much to be said about Web Services screenshots. There are lots of posts covering this topic and lots of different tools, including an Nmap plugin. Some references:

- Using Nmap to Screenshot Web Service (http-screenshot.nse)
PaulDotCom Security Weekly 295 - Tech Segment


EyeWitness - A Web Application Triage and Info-Gathering Tool


Conclusion

I find these tips very useful to get a better view of network services. Now that reporters are getting a pretty good idea from the attackers perspective, you have no excuse to leave your curtains exposed to the Internet without a VNC password. It's also important to practice safe computing, changing default passwords and enabling Network Level Authentication for RDP services.

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