This question is an exact duplicate of:
I have a Samsung Galaxy S3 with a broken screen. The screen does not respond to any touch and does not display anything at all, it is black at all times. CyanogenMod 11 is installed on the device.
I need to securely wipe the device, but I've been having a very difficult time doing so, as CyanogenMod doesn't allow ADB to connect without user input, which in this case is impossible. I've done a factory reset on the phone, but didn't wipe the user data on the internal storage (not an external SD card, rather the "internal SD card" which is hosted on the main phone ROM).
How can I securely wipe the phone and delete all data left on the internal storage? I'd like to zero-out the filesystem, but still have a semi-working phone that will at least boot into Android for occasional tinkering over adb.