Summary
Buffer overflows in user input dependent buffers have become one of the biggest security hazards on the internet and to modern computing in general. This is because such an error can easily be made at programming level, and while invisible for the user who does not understand or cannot acquire the source code, many of those errors are easy to exploit. This paper attempts to teach the novice - average C programmer how an overflow condition can be proven to be exploitable. Details1. Memory
Note: The way we describe it here, memory for a process is organized on most computers, however it depends on the type of processor architecture. This example is for x86 and roughly applies to Sparc. The principle of exploiting a buffer overflow is to overwrite parts of memory that are not supposed to be overwritten by arbitrary input and making the process execute this code. To see how and where an overflow takes place, let us look at how memory is organized. A page is a part of memory that uses its own relative addressing, meaning the kernel allocates initial memory for the process, which it can then access without having to know where the memory is physically located in RAM. The processes memory consists of three sections: - Code segment, data in this segment are assembler instructions that the processor executes. The code execution is non-linear, it can skip code, jump, and call functions on certain conditions. Therefore, we have a pointer called EIP, or instruction pointer. The address where EIP points to always contains the code that will be executed next. - Data segment, space for variables and dynamic buffers
Read more: Beyond security
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Buffer overflows in user input dependent buffers have become one of the biggest security hazards on the internet and to modern computing in general. This is because such an error can easily be made at programming level, and while invisible for the user who does not understand or cannot acquire the source code, many of those errors are easy to exploit. This paper attempts to teach the novice - average C programmer how an overflow condition can be proven to be exploitable. Details1. Memory
Note: The way we describe it here, memory for a process is organized on most computers, however it depends on the type of processor architecture. This example is for x86 and roughly applies to Sparc. The principle of exploiting a buffer overflow is to overwrite parts of memory that are not supposed to be overwritten by arbitrary input and making the process execute this code. To see how and where an overflow takes place, let us look at how memory is organized. A page is a part of memory that uses its own relative addressing, meaning the kernel allocates initial memory for the process, which it can then access without having to know where the memory is physically located in RAM. The processes memory consists of three sections: - Code segment, data in this segment are assembler instructions that the processor executes. The code execution is non-linear, it can skip code, jump, and call functions on certain conditions. Therefore, we have a pointer called EIP, or instruction pointer. The address where EIP points to always contains the code that will be executed next. - Data segment, space for variables and dynamic buffers
Read more: Beyond security
QR:
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