Chapter 25. Unix Kernel Overflows
In this chapter, we explore kernel-level vulnerabilities and the development of robust, reliable exploits for Unix kernels. A few generic problems in various kernels, which could lead to exploitable conditions, will be identified, and we present several examples from known bugs. After familiarizing you with various types of kernel vulnerabilities, we advance the chapter by focusing on two exploits that were found in OpenBSD and Solaris operating systems during the initial research conducted for this chapter.
The vulnerabilities we discuss result in kernel-level access to OS resources in all versions of OpenBSD and Solaris. Kernel-level access has the rather serious consequence of easy privilege escalation, and consequently, the total compromise of any type of kernel-level security enforcements such as chroot, systrace, and any other commercial products that provide B1-trusted OS capabilities. We will also question OpenBSD's proactive security and its failure against kernel-level exploits. This will hopefully give you the motivation and spirit to target other supposedly secure-from-the-ground-up operating systems.
Kernel Vulnerability Types
Many functions and bad coding practices exist that can lead to exploitable conditions in kernel land. We will go over these weaknesses and provide examples from various kernels, giving hints about what to look for when conducting audits. Dawson Engler's excellent paper and audit "Using Programmer-Written Compiler ...
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