Also known as write xor execute, W xor X
W^X (write xor execute, pronounced W xor X) is a security policy in operating systems and software frameworks. It implements executable space protection by ensuring every memory page (a fixed-size block in a program’s virtual address space, the memory layout it uses) is either writable or executable, but not both. Without such protection, a program can write (as data "W") CPU instructions in an area of memory intended for data and then run (as executable "X"; or read-execute "RX") those instructions. This can be dangerous if the writer of the memory is malicious.
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W^X (write xor execute, pronounced W xor X) is a security policy in operating systems and software frameworks. It implements executable space protection by ensuring every memory page (a fixed-size block in a program’s virtual address space, the memory layout it uses) is either writable or executable, but not both. Without such protection, a program can write (as data "W") CPU instructions in an area of memory intended for data and then run (as executable "X"; or read-execute "RX") those instructions. This can be dangerous if the writer of the memory is malicious.
The terminology was first introduced in 2003 for Unix-like systems, but is today also used by some multi-platform systems (such as .NET). Other operating systems have adopted similar policies under different names (e.g., DEP in Windows).