just to be more specific, I would like to know more about the system files that can be accessed with regards to a jailbroken phone.
From what I understand, each ios application has its own sandbox. A phone has root access once it is jailbroken, allowing creation of 3rd party system applications which result in accessing the system files. However, if I am not wrong, the sandbox is still there just that it has lesser restrictions hence allowing accessing of system files?(not sure about this part too).
So for a jailbroken phone, what kind of critical system files are we able to access from our created application that will go through the sandbox and which are not accessible from a unjailbroken phone? Is contact list a part of the critical system files, although I believe we are still able to get contact list without a jailbroken phone using the Address Book frameworks.
I may be wrong, but my term of Critical system files refers to system information that normal users would not like others to get hold of so I was thinking if contact list is part of it even though it does not require a jailbroken phone.
Without taking Tweaks into consideration, an app is able to read/write/execute in the root directory /. Tweaks are able to do whatever they want (just like the app would - even an Apple pre-installed app), depending on where they are hook-ing. For example, a tweak I was working on for MobileSMS (the SMS app) can give me the passcode of your iCloud account stored in the keychain by default.
Long story short, jailbreaks equals zero security for an average user. On the other hand, there is only one exploit (at least to my knowledge) currently, that attacked iOS and came from GeorgiaTech a few months ago, hidden in an app on the App Store.