Scripting Fake UITouch Events Using Frida and Lyft Hammer

Simulating or Sending Fake UITouch Events

I was having a ton of trouble reverse engineering this Swift app to get it to send a request to lock and unlock my door.

Long story short, it had some code to refresh the JWT it had in memory that I couldn't figure out how to trigger. And the JWT I could find was always old.

So I had the crazy idea of why not just modify the app so that when it opens, it waits a little bit for the app to load and then sends a fake touch event to the screen to press the button that triggered the request to lock/unlock the door.

Now there are a number of example's of how to do this. One by the great Frida creator himself.

If you just want a super nice and concise implementation of how this can be done checkout his repo here

However, before I found this I had only found Lyft's Hammer repo

Hammer is a little more complicated but has some useful functionality like the ability to wait for the touch event to be handled. So if you wanted to reliably script a chain of touch events you would probably want to use Hammer.

What ended up being the big issue here for me was the use of the XCTest framework.

I am pretty sure the XCTest framework is NOT supposed to be EVER deployed to an iOS app on your phone. Just for testing in simulator. Although I am not sure about this.

What I can say is that it is a dynamically linked library that has a ton of dependencies that your phone won't have. So if you do build a dylib from this Hammer repo. Inject the dylib into the app and then try to use it from Frida like I did. You won't be able to becuase XCTest has soooo many dependencies.

XCTest depends on XCTestCore which I think depended on XCTestSupport etc etc... There just a huge tree of dependencies basically coming off of XCTest.

NOTE: I did try just commenting out all the XCTest related code so I could remove the XCTest dependency. Neutering the wait functionality and this did work. I was able to create a dylib without any required dependencies where I could still send fake touch events.

I wanted that "wait for touch event to be registered" functionality though and went about trying to get all the dependencies in place.

This lead me to writing a tool that looks at a dynamically linked library and locates all of its dependencies from your machine, copies them into a folder and updates the rpath so they can find each other.

Ironically, after I did all this work I found there were some repos out there already doing similar, if not the same thing... Frustrating I didn't find this before.

This is all documented here and I would checkout the README if you are interested in a tool to help get a dependcy tree built when you have a depency like XCTest you want to inject into an iOS app.

Since Hammer is a Swift app though I had to create a whole Swift project with a bridging header to Objective C so that I could create an Objective C class with class methods I could easily call from Frida. This can be found here. Note that is a mess and has left over code form when I was trying to swizzle.

After injecting the dylib with my wrapper around Hammer and all of its XCTest deps I was able to script touch events using Frida with:

ObjC.classes["HandleURLScheme.BBEvent"]["+ sendTouchWindowAtX:y:"](0,0)

Note that 0,0 is the center of the screen