Question

What is an NX (no-execute) bit, and how can it be used to counter buffer overflow attacks?

Answer 1

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Solution:-

Let us first know about buffer overflow attacks.

An application with NX bit support may set certain memory locations as inactive(non-executable). The processor will be refusing to execute any code that resides in these memory locations. A standard procedure, known as executable space protection, is used to protect certain types of software that are malicious from taking computers by inserting their code into another program's data storage area and processing its own code within this section; this is known as a buffer overflow attack.

NX bit-  NX bit (no execute) is a technology used in CPUs to separate memory areas for use by keeping the instructions of the processor (code) commands or for storing data, a feature commonly found only in Harvard processors. However, the NX bit is still used continuously in von Neumann's standard processors for security reasons.

How can it be controlled-

Data Execution Prevention (DEP) is a security feature found in modern Microsoft Windows applications aimed at preventing an application or service from using the code from the memory location(non-executable memory region).

DEP for Hardware Deployment enables NX bit on compatible CPUs, with automatic use of PAE kernel for 32-bit Windows and traditional support for 64-bit kernels. Windows Vista DEP works by marking certain parts of memory as intended for data storage only, which the NX or XD enabled processor deems to be invalid(non-executable). This helps prevent the buffer overflow attack.

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