Ads Top

Demiguise - HTA encryption tool

The aim of this project is to generate .html files that contain an encrypted HTA file. The idea is that when your target visits the page, the key is fetched and the HTA is decrypted dynamically within the browser and pushed directly to the user. This is an evasion technique to get round content / file-type inspection implemented by some security-appliances. This tool is not designed to create awesome HTA content. There are many other tools/techniques that can help you with that. What it might help you with is getting your HTA into an environment in the first place, and (if you use environmental keying) to avoid it being sandboxed.

How does it do it?

This is achieved by encrypting the HTA file using RC4, and then using navigator.msSaveBlob to "save" the file at runtime - rather than fetching the HTA directly from the server. Meaning that at no point is there any HTTP request/response that contains your HTA file in a plain-text form - the proxy will simply see a text/html file containing your encrypted blob. In the latest version of Edge, this will result in the user being prompted to "run" the HTA.
Although not the primary aim of this tool, there are a couple of payload-options for the underlying HTA. Each option uses different techniques as previously documented by Matt NelsonMatthew DemaskeRyan Hanson and Etienne Stalmans. The benefit of using these techniques is that your code does not execute as a child of mshta.exe. As mentioned previously, the content of the HTA is not the primary aim of this tool. I'd encourage you to modify the HTA template to contain your own custom code :)

How do I run it?

Run the file, giving it your encryption-key, payload-type, output file-name and command that you want the HTA run.
Example: python -k hello -c "notepad.exe" -p Outlook.Application -o test.hta

Environmental Keying

In order to evade sandboxes, you shouldn't embed your key directly in the HTA. Instead you should get this dynamically from the environment the target is based in. An example of this may be to use the client's external IP address as a key. The benefit of this is that if the code is run in a 3rd-party sandbox, the HTA will not decrypt. In fact, the file-name will not even decrypt, meaning that nobody will know what your payload is/does :)
Powered by Blogger.