Questions tagged [c]
General purpose programming language that uses the procedural and structured programming paradigm.
229
questions
1
vote
2answers
82 views
How to solve this anti-disassembler trick?
I have this __asm instruction in C code:
int func_0x8b4c55a0()
{
__asm
{
call $ +5
add[esp],5
ret
}
}
int main()
{
char cVar1;
if ((cVar1 = ...
1
vote
1answer
86 views
Best way to protect source code of .exe program running on Python?
I am developing proprietary software that would be distributed in a form of .exe file. In order to use it, users will have to authenticate with their whitelist credentials (username + password).
The ...
0
votes
1answer
61 views
Abusing the strlen output
My question is related to the strlen function from the C and C++.
I am reversing a program, that reads a byte data from allocated memory and sends to the strlen directly. To be completely honest ...
1
vote
1answer
67 views
Why is fastcall used for replacing thiscall functions in memory instead of cdecl?
Assume I were to be reversing some game which processes all of it's movement client side and have determined some function to be of the type:
bool __thiscall Player::CanJump(Player *this)
that I ...
1
vote
1answer
95 views
mfc140 dll , what is the usage?
While I open exe file in ida I can see lot of calls to mfc140_6153
or mfc140_8718.
What are those functions ? what they do ?
thanks
0
votes
0answers
79 views
What is, and why, “byte[ ] + number” in this IDA pseudocode?
This is a decompile of an .so file, so it originated from C or C++. Can you kindly try to explain to me what this does?
How would one rewrite this into readable code? I don't mind any programming ...
2
votes
1answer
123 views
Unable to properly analyze a very simple C-compiled program
I'm a RE beginner and I decided to start writing my own simple code for practice.
I wrote a simple code which uses a winAPI function called CreateProcess to start a calc.exe, I've wrote it in C and ...
1
vote
2answers
202 views
Local variables and addition not shown in Ghidra
I am having some troubles with my learning of Assembly and reverse engineering. Specifically, I am learning about Global vs Local variables. For Global variables I have managed to get insights in ...
2
votes
1answer
359 views
Simple C program disassembled with Ghidra
I am trying to figure out what is going on with my simple example programs, when I disassemble them with Ghidra. I am not sure whether this is some strange Ghidra behaviour or something that is set by ...
-1
votes
1answer
167 views
What is the following assembly code doing? [closed]
str fp,[sp, -4]!
add fp, sp, #0
sub sp, sp, #12
str r0, [fp, #-8]
str r1 [fp, #-12]
L5:
ldr r3, [fp, #-8]
ldrb r3, [r3]
cmp r3, #0
beq .L2
ldr r3, [fp, #-12]
ldrb r3, [r3]
cmp r3, #0
beq .L2
ldr r3, [...
0
votes
1answer
151 views
Can we hook the Nt or Zw functions using IAT hooking, or just inline hooking?
So i was trying to hook the ZwQuerySystemInformation or NtZwQuerySystemInformation using IAT, but i found out that these are not inside the IAT inside the memory nor in the PE file
but maybe i am not ...
-1
votes
1answer
93 views
Understanding (pseudo-)C function from a video game [closed]
I recently found a function using IDA within a game that creates a CRC from a string. I don't understand much of the code or how the game takes in the string as data.
__int64 __fastcall ITF::...
0
votes
0answers
37 views
Add MessageBox statically modify
So i'm doing this challenge which i have an exe file and a dll all i have to do is
modify it statically to pop a MessageBox.
The exe file is loading the dll which load the MessageBox, with ollydbg ...
1
vote
2answers
131 views
Elf x86_64 adding function
I'm trying to see if I can append function code in the .text section of an ELF while still maintaining the execution flow of the original ELF. Ideally, I want to call the new function but that's it's ...
0
votes
2answers
98 views
Unable to exploit format string vulenrability on Ubuntu 18.04.2 LTS
I am studying from "Hacking: The Art of Exploitation" and in program fmt_vuln.c format string is exploited. I am getting Segmentation Fault error.
Checking position of AAAA on stack:
$ ./fmt_vuln ...
0
votes
0answers
37 views
Examining Stack Frame in GDB
I am learning exploitation from the book "Hacking: The Art of Exploitation". In the program an integer variable auth_flag is declared after a char array password_buffer. So on stack frame first ...
1
vote
0answers
77 views
Static binary instrumentation
I am working on a class project. I need to find out static features of a program (without executing it).
Backward branches (loops)
Conditional branches (potential threads with load imbalance)
...
1
vote
1answer
189 views
How to pass param to execve to execute cat a file in x64 Asm? [closed]
I want execve("/bin/cat",["/bin/cat","/test/file"],NULL).
Here is my asm
xor %rdx, %rdx
push %rdx
sub $0x16, %rsp
movb $0x2f, 7(%rsp)
movl $0x2f6e6962, 8(%rsp)
movl $0x746163, 12(%rsp)
leaq 7(%rsp)...
1
vote
2answers
124 views
Trouble when reverse engineering a industrial robot software in order to get some values
For the bit of background, I'm a robotic engineer.
Robotics manufactures hide some parameters of their robots in order to avoid their competition. Now, I need these data to compute the dynamics model ...
1
vote
0answers
65 views
Reconstructing struct/union-based IPC protocol wire format
I'm embarking on my first reverse-engineering adventure. I think I've picked a rather dense piece of steak to start out with.
I have three C programs which communicate together using an unknown IPC ...
2
votes
1answer
380 views
Reverse a call to mmap()
I am currently reverse a challenge to learn. But why is the parameter of mmap (containing fd) at 4294967295?
(Is it not supposed to exist? No files are open with open, just before.)
1
vote
0answers
141 views
Mysterious chunk of code in IOLI crackme0x06 challenge
I've been struggling to understand a very strange piece of x86 assembly code from the IOLI crackme0x06 challenge.
Context
But first of all, here is the context : I've successfully cracked the ...
3
votes
2answers
150 views
x86 shellcode leads to segmentation fault
I want to execute execve("/bin/dash", &"/bin/dash", NULL) on Ubuntu 64 bit with the following 32 bit shellcode:
global _start
_start:
xor eax, eax ; set eax = 0 to push a null without using ...
0
votes
1answer
500 views
Ghidra pseudocode to Java/C
I have this piece of code generated from Ghidra
void __cdecl FUNCTION(uint *key,uint *text)
{
undefined uVar1;
ushort uVar2;
uint *puVar3;
uint *puVar4;
uint *puVar5;
int iVar6;
uint ...
3
votes
1answer
91 views
How to find the index of static ilbrary functions in the PLT of the binary?
So right now I'm trying to resolve function calls and their names in my reversing tool
the problem I'm having is that library functions such as printf and fwrite and such do not have a corresponding ...
1
vote
3answers
137 views
Is the main function's name in the symbol table of C & C++ programs always 'main'? if not, how to find the name?
So I'm trying to write a reversing tool that parses symbol table to find the main function's address
right now all the binaries I'm checking the name of main function is still main in symbol table
...
0
votes
0answers
29 views
Changing pseudocode based on FPU fmul behaviour
A 3D software was compiled in which a typical x/4096f was translated as:
fmul ds:f4096
where f4096 equals to: 0.00024414062
Example decompiled pseudocode as-is:
skeletonMemoryPointer[i].pos = *(...
-1
votes
1answer
106 views
Fuzz Test Suite for C/C++ Command Line Argument/Standard Input programs
I have implemented a basic coverage guided fuzzer that is sending inputs to programs accepting ONE command line argument or ONE standard input. I am trying to find a complex code to fuzz that can meet ...
3
votes
1answer
74 views
GetWindowLongPtr with undocumented nIndex of -1
I'm trying to reverse functionality of scrollbars in comctrl32.dll and I keep witnessing them calling GetWindowLongPtr function with undocumented index -1 as such:
Does anybody know what that ...
1
vote
0answers
231 views
Illegal instruction fault in stack based buffer overflow
I wrote this short C program to practice buffer overflow exploits:
#include <stdio.h>
#include <string.h>
#include <stddef.h>
#include <inttypes.h>
char *decode(char *s){
...
3
votes
0answers
161 views
Reverse engineering android native packer
im trying to Reverse engineering an android app and the app have 4 folders in the /data/data/{package} folder
├───app_dexprotector
│ 823517D25836B88F1C499C02370A047E.dat
│ ...
-1
votes
1answer
150 views
How can I convert the following assembly code to pseudo code?
I got the following disassembly code in IDA pro. I really find it hard to convert it into pseudo code.
push ebp
mov ebp, esp
sub esp, 14h
mov dword ptr [ebp-14h], 1
mov dword ptr [ebp-10h], 2
mov ...
-1
votes
1answer
140 views
How can I convert the following disassembly code to pseudo code or C code?
I used IDA pro to get the following disassembly code. I am having difficulty converting it into the equivalent c code.
mov dword ptr [ebp-8], 1
mov dword ptr [ebp-4], 0
loc_401014:
cmp dword ptr [...
4
votes
1answer
147 views
Reverse engineering a compression algorithm to decompress ASCII text (LZ-variant?)
Reposted from StackOverflow as is.
I'm trying to decompress a very long text block from an ARMv5t powered Gameboy Advance ROM, which was compressed using some kind of custom LZ-esque compression ...
0
votes
1answer
148 views
Is there any decompiler, which can produce a compilable result?
I would like to decompile a 32bit linux executable to C, modify some parts of it, and then compile it back. I do not care if the C code is not pretty and really hard to maintain. The only thing I care ...
1
vote
1answer
111 views
(CTF) Speed up assembly by hooking to an static function
For a CTF I have a fairly slow recursive function. I just need to cached the previous results in a dictionary and get them instead. I did it but had to reverse engineer the code. I was wondering if ...
-1
votes
2answers
249 views
CreateThread returns true but thread doesn't run [closed]
I have a PE executable which uses threads to handle most of its functionality. It uses CreateThread API to spawn local threads to handle functions.
The call to the CreateThread returns a valid handle ...
5
votes
2answers
873 views
Which operators use sal, shl, sar or shr
Which operators in C language would result in assembly commands such as sal, shl, sar or shr for example?
0
votes
1answer
147 views
why code at .rodata executes [closed]
How come the following code executes if buf* is @ rodata segment ?
#include <stdio.h>
char *buf[] = {
"\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\
\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\...
1
vote
1answer
243 views
How int3 looks like in C
This is assembly code that can catch debugger with int 3 :
MOV ECX, ExceptionHandler
MOV DWORD PTR FS:[0], ExceptionHandler
INT3
///there is debugger!!!
ExceptionHandler:
////no ...
-2
votes
1answer
394 views
Why dont use memcpy? [closed]
Why using memcpy can cause to stack overFlow?
memcpy get the number of bytes to copy, so what is the problem , and how memcpy_s fix it?
2
votes
2answers
303 views
Why are there so much more functions in ida than my source code?
I am trying to learn how to use IDA Pro 6.8 to analyze binaries. However, there are much more functions in ida function list than my code. For example, there is a function in source code that calls ...
-1
votes
1answer
1k views
How to convert assembly to pseudo code? [closed]
I have the following assembly. I don't know how to follow assembly. I was wondering if there is a way to convert assembly to a human readable pseudo code or better yet C code:
init:
mov eax, [ebp+...
0
votes
1answer
322 views
How can I intercept syscall libc function in C++ without writing any code in C file
How can intercept libc function in C++ using LD_PRELOAD. I want to write code only in C++ file and all the logic of symbol fishing (dlsym) must be in C++ file.
Please give an example.
2
votes
1answer
161 views
Finding the main function without symbols
for a C/C++ program compiled on windows using the x86 architecture, what is the best way to find the main function within disassembled code?
I've found various answers to questions similar to this, ...
-2
votes
1answer
230 views
Can someone please help me reverse engineer this assembly code to C please! [closed]
I am really bad at understanding assembly code and the way it works. I have little problems given to me in Assembly code and I have to reverse engineer it to C, but I have been doing really bad job at ...
0
votes
1answer
128 views
Changing local variable in caller from callee in C?
I'm implementing a function which is going to perform some time-consuming task, and I'd like to hack the benchmarking part a bit by changing the variable indicating the CPU time my function has ...
1
vote
1answer
2k views
What does this assembly language program output?
I have been struggling with this for a long time. I have the following assembly language code:
.intel_syntax noprefix
.bits 32
.global asm0
asm0:
push ebp
mov ebp,esp
mov eax,DWORD ...
-1
votes
1answer
466 views
How can I decompile the CC2650 .hex file to C?
I want to decompile it to C, or at least assembly the CC2650 hex file (Bluetooth Low Energy Sensor Tag), that provide TI.
My goal is to know the specific way used by CC2650 to generate the LTK.
I'll ...
8
votes
4answers
14k views
Purpose of test eax,eax after a strcmp
This is my first program i am trying to reverse and my intro to this field.
The C program will test if two strings match, and it will printf() a message for each occasion.
This is what the reversed ...
