Firebase Domain Front - Hiding C2 as App traffic
We often see that large organization use firebase for hosting their applications and database. Firebase has a lot of features such as real-time database, hosting, cloud functions, hosting etc. Today we are going to talk about firebase hosting and cloud functions which are used by a lot of mobile applications these days. In our recent project, we were able to hide ourselves as a legit mobile traffic and bypass a lot of traffic filters
Firebase Cloud Functions

Firebase allows an operator to write an applications in Node JS and deploy it using its hosting feature.
Setting up Firebase Domain Front
So lets start by selecting a app hosted using firebase. In the following case we'll take https://go.auk.eco/ as our selected app.
Step 1: Create an account on https://firebase.google.com
Step 2: Go to Console

Step 3: Create a project and give it a name



Step 4: Open your command prompt and install firebase cli.
Step 5: Make a folder and perform firebase cli login.
Step 6: Initiate Hosting
Once you hit the above command you'll be presented with many options. See the following screenshot for responses to the options

Step 7: Initiate Cloud functions
Again you'll be presented with many options. See the following screenshot for the response to the options

Step 8: Install Express and http-proxy

Step 9: Edit the index.js
Since you are already in the functions folder after saving the npm packages. Lets edit the index.js file in this folder.
Step 10: Edit the firebase.json file
Go to the parent folder and edit firebase.json
Step 11: Deploy the project
Lets start the deployment of our firebase project

Modify the plan of project from free plan to Pay as you go plan


Now lets try the deployment again.

Final Tests for the Domain Front
Lets check what's hosted on https://firebase.redteam.cafe/api/index.html

Let's check if our app works fine

THE FINAL TEST
Lets see if we are able to do Domain Front against a test domain https://go.auk.eco/

How to Find more domain fronts
Hint: Try to find domains whose CNAME ends with *.web.app
UPDATE (4/5/2021) : Vincent Yiu created a list for domain fronts in the following github repo
https://github.com/vysecurity/DomainFrontingLists
Download Source Code
Source code can be downloaded from my github repository https://github.com/shantanu561993/Awesome_Firebase_DomainFront
Credits
Connect with me
Twitter: https://twitter.com/shantanukhande
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