debugging a CEF Browser Window

[mightee]

Hi there, I am new to this forums. I am looking for help for the following situation:

I am starting new at a web agency. I am assigned to make changes to a CEF app, which the company contracted. The company does not have the source code but they know (I also checked it with winspector) that the application (windows) is based on CEF. A main exe file is calling this CEF browser window, so I cant actually start it with --remote_debugging_port=1234. I need to debug this app and inject some JS so that the UI looks different. As we dont have the source code and the contractor is not reachable in any way, I wanted to ask you guys if there is any way to inject some JS to the CEF app. debugging would also suffice. any ideas ?

[magreenblatt]

Without source code, which would likely be required to rebuild the app, how do you plan to fix it once you've debugged the problem?

[mightee]

well i was hoping to inject the JS every time the program is started. i am out of options right now.

[magreenblatt]

well i was hoping to inject the JS every time the program is started. i am out of options right now.

If the app is installed and run in the usual way then that's unlikely to be a viable solution. If you can instead run the app using a custom bootstrap script then you could start it with remote-debugging enabled and then use a separate application to connect via the DevTools protocol and control/modify the app. See https://chromedevtools.github.io/devtools-protocol/ for details on the DevTools protocol.

[mightee]

hmm in order to do that, i need to somehow figure out, whit what kind of parameter the cef browser window is being started. do you know any program which looks for arguments that a program takes in ?

[magreenblatt]

The expected command-line flag is "--remote-debugging-port=1234" (note the slashes). Try that.

[mightee]

well there are 3 exe files.
- AppName.exe
- AppUx.exe
- AppUxRender.exe

only appname.exe file shows something. the other exe files wont do anything. i guess they need some arguments to be passed.

--remote-debugging-port=1234 didnt change anything.

[mightee]

anyone ?

[magreenblatt]

Sorry, I don't have any additional advice for you. You're effectively trying to reverse-engineer a closed source application. I suggest you instead talk with the client about either getting the source code or recreating the application.