Contents
What is ESP in buffer overflow?
ESP: Stack pointer. EBP: Base pointer. ESI: Source Index holds the location of input data. EDI: Destination Index points to the location where the result of data operation is stored. EIP: Instruction Pointer.
What does JMP ESP mean?
Putting it simply, ‘JMP ESP’ means ‘Jump to the ESP register. ‘ We will place our shellcode on top of our stack frame, for that reason we need the memory address of JMP ESP.
What is a bad character?
Filters. A person’s predisposition to commit evil acts. noun.
What are ESP and EBP?
ESP is the current stack pointer. EBP is the base pointer for the current stack frame. When you call a function, typically space is reserved on the stack for local variables.
Does JMP modify the ESP register?
In the x86 assembly language, the JMP instruction performs an unconditional jump. Such an instruction transfers the flow of execution by changing the instruction pointer register.
Why does jmp esp need to be used for C buffer overflow?
This is a problem because the zero byte is a string terminator in C/C++, and using zero bytes as part of strings used to overflow a buffer will often result in the string being terminated at that point, potentially preventing the buffer from being appropriately overflowed and breaking the exploit.
Why do jmp esp instead of directly jumping into the stack?
We have to find a way to jump to our buffer to execute our code. ESP points to the beginning of the C part of our buffer. We have to find a JMP ESP or CALL ESP instruction. Do not forget, that the address must not contain bad characters! This makes sense, but; Wouldn’t be possible and easier to directly jump into the stack since we control EIP?
Why are 4 bytes passed to EIP at JMP ESP?
But after the buffer has been overflown, EIP has no idea where to point at. Note that, the 4 bytes we pass to EIP can be any of the [jmp ESP] addresses. I wrote an exploit and used variations of address at [jmp ESP] and each time i could exploit the vulnerability.
How to avoid buffer overflow securable OSCP cheat sheet?
Check if not being affected by any memory protection schemes (Rebase, SafeSEH, ASLR, NXCompat) and note the specific DLL (right column). Step 9: JMP ESP equivalent = opcode. Step 10: use mona to find the JMP ESP memory address within the DLL found in step 8. Use one which does not contain any bad chars.