Thursday 11 July 2013

Remember to removePIE...

A couple of weeks back I was reversing an app and trying to work out what it was doing. I had removed the encryption (the short hand way) using clutch and had the class-dump-z output, but this wasn't quite enough. I needed to go a bit deeper  as I wanted to know a bit more about what was going on.

I already had GDB installed on the device so I decided to spark the application up and attach to the running process. This all went well, I then set my self a couple of breakpoints which seem to be excepted. I hit C and continued to debug the app. Each time the app got to the point I was expecting it to stop it would just keep going. Hmmm odd, maybe GDB isn't working quite right, I'lll try LLDB.

I configured LLDB to work remotely and started a session on my laptop, once again configuring the break points I wanted. Again the app just continued to run no problems, wtf. This was getting frustrating, had the developer configured some anti debug tactics. I had a look around and I wasn't seeing any "Segmentation fault: 11" errors on attach so I assumed they hadn't. Both GDB and LLDB were just not stopping on any of the breakpoints I had set.

After much searching, I came across another blogpost that simply said "Can you debug iOS applications if ALSR is set". A £2 coin hit the floor, boom. I had forgotten disable the ALSR protection. I downloaded removePIE from here, copied it to my device and ran against the app.

Bingo, my breakpoints were being hit and working perfectly on both GDB and LLDB. I won't forget this again...

If you want to know more about disabling ALSR and how it works check out the right up here


  1. can you make a post about how you did the remote lldb debugging ?

    1. Already done, check earlier post on remote LLDB debugging. Thx. //56k