NX-DEP (No-eXecute)

Updated 13 Sep 2026

•
What it is
- •
  NX/DEP prevents instruction execution from pages without execute permission. It does not itself forbid a page from being both writable and executable; that is the separate W^X policy.
•
How it works
- •
  Read, write, and execute permissions are separate. The CPU checks the effective page permissions when accessing memory.
- •
```
rw- page → data can be written, but instruction execution faults
rwx page → writing and instruction execution are both permitted
```
•
When to use it
- •
  An NX-protected stack blocks code execution there; inspect mappings before choosing Shellcode or existing-code reuse such as ROP Chain.
- •
  A challenge may explicitly allocate an RWX input buffer even when other mappings are non-executable.
- •
  An executable stack permits stack-resident shellcode; it says nothing about the permissions of other regions.
•
Examples
- •
  Shellcode on an rw- stack faults when executed. An explicitly mapped rwx challenge buffer permits execution.
•
pwntools
- •
```
elf = ELF('./vuln')
print(elf.nx)
```

Debugging

checksec
vmmap        # inspect per-page R/W/X permissions