Uploading files to RDP when that is restricted

The short version:

  • A tool which works in Kali Linux which will “upload” a file to an RDP session.
  • Most of the time RDP allows one of “drag and drop”, “copy and paste”, or “mounting of your local hard drive”. So 99% of the time you do not need to do this at all!
  • When all other options are unavailable to you then you can always simply type the contents of any file you want. Then use built in tools on the target’s side to decode and then execute your uploaded file.

Get the tool here:

https://github.com/cornerpirate/rdpupload

With an example usage embedded below:

Details

This is a very old technique. All I have done is have a stab at making my own tool for doing this. I meet aspiring hackers who say they want to jump into coding, but don’t have any “ideas”. They seem unimpressed when I say write a port scanner.

If that is you then I say to you: re-invent the damn wheel!

Sometimes the wheel needs upgrading you know? Many of the tools we have now as the “goto” for something are about 17th in newness of technique. Any tool can be toppled by a better successor.

But world domination is not the goal. Implementing your own versions of old ideas is actually just for getting your skills in for the day you invent an entirely new wheel. It also teaches you how a thing works which is brilliant. At a job interview you will stand out if you actually know what the top tool does under the hood.

What I learned on this one

To make rdpupload I have learned:

  • argparse better (I have used this before)
  • how to simulate key presses in python
  • how to do a progress bar in a CLI
  • how to zip a file using python
  • how to play an mp3 in python

But most importantly I learned how a file upload may work by typing it, along with how to decode that on the server side easily.

Technique Used

The following summarises the techniques used:

Kali Side:

  1. Zip the file you want to upload (might save some characters depending on the file).
  2. Base64 encode that file (so every character we are going to use is available on a standard English Keyboard).
  3. Split the encoded file into chunks of size 256 characters (arbitrary length choice here).
  4. Spoof a keyboard typing each block of 256 characters until it is completed.
  5. Display a progress bar and optionally play the sound of a typewriter hammering away while the “upload” happens.

Victim Side:

  1. Place the cursor into “Notepad” within an RDP session.
  2. When the “upload” is complete save that as a “.txt” file.
  3. Open a command prompt and use “certutil.exe” to decode the base64 encoded file. The syntax for that is shown below.
  4. Use the zip feature of Windows to unpack the zip file.
  5. Profit.

The decoder on the server side relies on “certutil.exe”. Unless I am wrong this is available from Server 2003 upwards so is pretty useful for most use cases.


Syntax: certutil -decode <inputfile> <outputfile>

Example: certutil -decode nc.txt nc.zip

The decode command is also spat out on the Kali side for convenience once the upload is complete.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s