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What is shellcode?
Shellcode is the code we want to upload to the remote system
Our "evil code"
It is a set of instructions injected and executed by exploited software
In hacking, a shellcode is a small piece of code used as the payload in the exploitation of a software vulnerability. It is called "shellcode" because it typically starts a command shell from which the attacker can control the compromised machine, but any piece of code that performs a similar task can be called shellcode.
How does a shellcode work?
Native code which perfoms a certain action (like starting a shell)
What are the proerties of shellcode?
Should be small
Because we maybe have small buffers in the vulnerable program
Don't know where it will be loaded in the vulnerable program
No Null Characters (0x00)
Strcpy etc. will stop copying after Null bytes
Don't reference anything outside of shellcode
What are syscalls, why do we use them, what are the alternatives?
In a syscall we ask the kernel to do something for us
Makes it easy to create shellcode
Direct interface to the kernel
Call LIBC code; write()
Problem: Don't know where write() is located!
What is a syscall (acording to man page)?
The syscall (system call) is the fundamental interface between an application and the Linux kernel.
What can be controlled with a syscall in a process?
create process (for example, fork)
get/set process attributes
wait for time, wait event, signal event
allocate, free memory
Name some things that can be done with syscalls in regard to file management.