University of Twente Student Theses


XNU : a security evaluation

Keuper, D. (2012) XNU : a security evaluation.

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Abstract:The XNU kernel is the kernel that powers Apple's OS X and iOS operating system. Originally developed by Next, but later acquired by Apple it has been around for more then twenty years. It is only since the introduction of code signing on iOS that hackers have developed a real interest in XNU. Prior to iOS 2.0 only a handful of articles were published on XNU in the context of security. In the past few years the interest of hackers increased by the popularity of jailbreaking (the process of removing the security restrictions of iOS) and iOS security is often discussed at the various security conferences. The interest of hackers in the XNU kernel has not gone unnoticed by Apple, which started to harden the security of their XNU kernel. In the latest releases of their operating systems they added different mitigation techniques such as kernel ASLR. The latest release of OS X (Mountain Lion) and iOS (6) are hardened with new protection mechanisms, which should reduce the risk of successful exploitation. In this thesis we describe all techniques that are meant to protect the kernel from attackers and their implementation. We argue the effectiveness of those techniques and how an attacker might try to circumvent them. We conclude this thesis with a comparison with other kernels, our opinion on the current security state of the XNU kernel and some recommendations on how to further improve the security. We state that the XNU kernel has many protection mechanisms in place, but that they could be improved to better protect against exploitation. Furthermore we state that the current design of XNU, which consists of two separate compo- nents that heavily interact, is error prone and would benefit from refactoring.
Item Type:Essay (Master)
Certified Secure, the Netherlands
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:54 computer science
Programme:Computer Science MSc (60300)
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