Changes in iOS 7 Security Make Kernel More Vulnerable to Attack
The security flaw involves the random number generator Apple uses to secure its kernel. In iOS 6, the number generator that encrypted the kernel derived its values in part from the CPU clock counter. Because it was based on time, the encryption was only marginally secure as the output values were predictable, especially when examining successive numbers.
Apple was aware of the limitations in iOS 6 and attempted to tighten security in iOS 7 by changing the random number generator to a linear congruential generator, which is more susceptible to brute force attacks.
The problem with the new generator in iOS 7 is that it uses a linear recursion algorithm, Mandt said, which has "more correlation" between the values it generates. That makes them easier to extrapolate and guess, he said.This flaw potentially allows a malicious hacker to gain kernel-level access to an iOS device via an unpatched vulnerability. The kernel is the base part of the iOS operating system and controls low-level functions such as security and resource allocation.
Apple approached Mandt about his findings and asked for his CanSecWest slide presentation.