关于RET覆盖型攻击中漏洞函数的epilog、prelog及成因代码排查请求

Alright, let's break this down step by step since you already have a working exploit for the RET overwrite attack—great job getting that far! To find the prolog and epilog of the function triggering this vulnerability, here's how I'd approach it:

Step 1: Locate the Vulnerable Function #

First, you need to pin down which function is allowing the stack overflow that overwrites the RET address. You can use either dynamic debugging or static analysis:

• Dynamic Debugging (e.g., GDB, x64dbg):
  • Set breakpoints on unsafe functions like gets(), strcpy(), strcat(), or scanf()—common culprits for unbound input. When your exploit triggers the overflow, check the call stack to see which parent function is calling these unsafe routines.
  • Alternatively, set a breakpoint on the ret instruction across the binary. When the overflow hits, the debugger will pause when the corrupted RET address is about to be executed—you can then backtrack up the stack to find the function whose stack frame was overwritten.
• Static Analysis (e.g., IDA Pro, Ghidra):
  • Scan the binary for functions that handle user input without length checks. Cross-reference calls to unsafe string/memory functions to find their parent functions.

Step 2: Identify the Function's Prolog #

Once you've found the vulnerable function, its prolog is the sequence of assembly instructions at the very start that sets up the stack frame. On x86 systems, this almost always looks like:

push ebp
mov  ebp, esp
sub  esp, 0x[hex_value]  ; Allocates space for local variables on the stack

On x64 systems, the prolog will be similar but use 64-bit registers:

push rbp
mov  rbp, rsp
sub  rsp, 0x[hex_value]

The key thing here is that the sub esp, ... (or sub rsp, ...) line reserves space for local buffers. If the input you're sending exceeds this reserved space, it will overflow into the saved EBP/RBP register, then the RET address—exactly the behavior your exploit is leveraging.

Step 3: Identify the Function's Epilog #

The epilog is the sequence at the end of the function that tears down the stack frame and returns control to the caller. For x86, this typically is:

mov  esp, ebp
pop  ebp
ret

For x64:

mov  rsp, rbp
pop  rbp
ret

The ret instruction here is what reads the value at the top of the stack (the RET address) and jumps to it. When your exploit overwrites this address with your shellcode, this ret is what triggers the execution of your payload.

Quick Verification #

To confirm you've got the right function:

• In a debugger, when the overflow occurs, check the stack before the ret executes. You should see your shellcode (or the address pointing to it) where the original RET address should be.
• Cross-check the prolog's stack allocation size against the length of input needed to trigger the overflow—they should align (input length > buffer size + size of saved EBP/RBP + size of RET address).

内容的提问来源于stack exchange，提问作者Muhammad Ahsan