Software Emulation of Feature
Prior to the onset of this feature within the hardware, various operating systems attempted to emulate this feature through software, such as W^X or Exec Shield. They are described later in this article.
An operating system with the ability to emulate and/or take advantage of an NX bit may prevent the stack and heap memory areas from being executable, and may prevent executable memory from being writable. This helps to prevent certain buffer overflow exploits from succeeding, particularly those that inject and execute code, such as the Sasser and Blaster worms. These attacks rely on some part of memory, usually the stack, to be both writable and executable; if it is not, the attack fails.
Read more about this topic: NX Bit
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