MiniDumpWriteDump via Faultrep!CreateMinidump

I found out this old undocumented API “CreateMinidumpW” inside the faultrep.dll on Windows XP and Windows Server 2003. This API ends up calling the dbghelp!MiniDumpWriteDump to dump the process by dynamically loading the dbghelp.dll on runtime.

The function takes 3 arguments. I really have no clue what this 3rd argument’s structure is. I passed 0 as the pointer to the structure so by default we end up getting 0x21 as the MINIDUMP_TYPE.

CreateMinidumpW(DWORD dwProcessId, LPCWSTR lpFileName, struct tagSMDumpOptions *)


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Running Shellcode Directly in C

Here’s a cool thing I figured out in position-independent code. I would rephrase the title as running position-independent code instead of shellcode. Check my previous article Executing Shellcode Directly where I used a minimal PE and pointed the AddressofEntryPoint to the beginning of the PIC.

So the goal is to run shellcode in C without any function pointers or any functions at all, not even a main function 🙂 For example, this is all the code. I declare the variable name as “main”. I am using the Microsoft’s Visual C compiler with no parameters.

char main[] = 
"\x90\x90\x90\x90\x90\x90\x90\x90\x31\xdb\x64\x8b\x7b\x30\x8b\x7f"
"\x0c\x8b\x7f\x1c\x8b\x47\x08\x8b\x77\x20\x8b\x3f\x80\x7e\x0c\x33"
"\x75\xf2\x89\xc7\x03\x78\x3c\x8b\x57\x78\x01\xc2\x8b\x7a\x20\x01"
"\xc7\x89\xdd\x8b\x34\xaf\x01\xc6\x45\x81\x3e\x43\x72\x65\x61\x75"
"\xf2\x81\x7e\x08\x6f\x63\x65\x73\x75\xe9\x8b\x7a\x24\x01\xc7\x66"
"\x8b\x2c\x6f\x8b\x7a\x1c\x01\xc7\x8b\x7c\xaf\xfc\x01\xc7\x89\xd9"
"\xb1\xff\x53\xe2\xfd\x68\x63\x61\x6c\x63\x89\xe2\x52\x52\x53\x53"
"\x53\x53\x53\x53\x52\x53\xff\xd7";

After compiling it won’t of course run. Why? Well, the initialized data will end up in the “.data” section.


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Converting an EXE to a DLL

I’ve been doing some crazy experiments on running an EXE as a DLL. Here are some parts of my research.

Case #1

Let’s take a simple example like a MessageBox.

#include <windows.h>

int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPWSTR    lpCmdLine,
                     _In_ int       nCmdShow) 
{
	MessageBox(NULL, L"@OsandaMalith", L"https://osandamalith.com", MB_ICONINFORMATION | MB_OKCANCEL);
  
}

After compiling to an EXE we have to change the characteristics under NT Header->File Header to a DLL file. I will use the value 0x2000 | 0x2| 0x100 = 0x2102.

#define IMAGE_FILE_DLL                       0x2000  // File is a DLL.
#define IMAGE_FILE_EXECUTABLE_IMAGE          0x0002  // File is executable
#define IMAGE_FILE_32BIT_MACHINE             0x0100  // 32 bit word machine.

typedef struct _IMAGE_NT_HEADERS {
    DWORD Signature;
    IMAGE_FILE_HEADER FileHeader;
    IMAGE_OPTIONAL_HEADER32 OptionalHeader;
} IMAGE_NT_HEADERS32, *PIMAGE_NT_HEADERS32;

typedef struct _IMAGE_FILE_HEADER {
    WORD    Machine;
    WORD    NumberOfSections;
    DWORD   TimeDateStamp;
    DWORD   PointerToSymbolTable;
    DWORD   NumberOfSymbols;
    WORD    SizeOfOptionalHeader;
    WORD    Characteristics;
} IMAGE_FILE_HEADER, *PIMAGE_FILE_HEADER;

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Random Compiler Experiments on Arrays

One day a guy asked me how to print a 2d string array in C. So I coded an example for him. But just for curiosity, I examined the assembly code. In C both string[0][1] and *(*string + 1) are the same. But in reality, the compiler writes the assembly code in 2 different ways. If we use string[0][1] it will directly move the value from the stack. When we dereference a pointer *(*string + 1) it will actually dereference the address pointed inside the register. This happens only in the MinGW GCC compiler. I compiled this using the latest on Windows which is 8.2.0-3 by the time I am writing this.

The assembly code in the left is this one.

#include <stdio.h>

int main() {
    char *string[][2] = { 
     {"Osanda","Malith"},
     {"ABC","JKL"},
     {"DEF","MNO"}, 
};

	printf("%s %s\n", string[0][0], string[0][1]);
}

The assembly code on the right is this.

#include <stdio.h>

int main() {
    char *string[][2] = { 
     {"Osanda","Malith"},
     {"ABC","JKL"},
     {"DEF","MNO"}, 
};

	printf("%s %s\n", **string, *(*string + 1));
}

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Analyzing an AutoHotKey Malware

I found this malware spreading through the Facebook messenger. Thanks to Rashan Hasaranga for notifying me this in the first place. It was targeting Sri Lankan people on Facebook. It was a compressed “.bz” file which was spreading via the messenger. The name had “video_” and a random number.

After I downloaded the files, I checked the file hashes. I couldn’t find any analysis done before. So, I decided to get to the bottom of this. The malicious files have the extension as “.com” instead of an exe. However, it’s a compiled exe, renaming this to “com” will still run as an exe by the Windows loader.

These are the samples I found. However, they all contain the same malware. I found 2 authors compiled this from 2 different machines. Read along 😊
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Linux Reverse Engineering CTFs for Beginners

After a while, I decided a write a short blog post about Linux binary reversing CTFs in general. How to approach a binary and solving for beginners. I personally am not a fan of Linux reverse engineering challenges in general, since I focus more time on Windows reversing. I like windows reverse engineering challenges more. A reason me liking Windows is as a pentester daily I encounter Windows machines and it’s so rare I come across an entire network running Linux. Even when it comes to exploit development it’s pretty rare you will manually develop an exploit for a Linux software while pentesting. But this knowledge is really useful when it comes to IoT, since almost many devices are based on Linux embedded. If you want to begin reverse engineering and exploit development starting from Linux would be a good idea. I too started from Linux many years ago. Saying that since some people when they see a reverse engineering challenge they try to run away. So if you are a newbie I hope this content might be useful for you to begin with.

The ELF Format

Let’s first have a look at the ELF headers. The best way to learn more about this in detail is to check the man pages for ELF.

Here’s in more detail. The “e_shoff” member holds the offset to the section header table. The “sh_offset” member holds the address to the section’s first byte.
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Haxing Minesweeper

Recently I tweeted a screenshot where I won the Minesweeper game by looking at the mine field from the memory. I posted this for no reason, just for fun since I was happy that I finally won this game. I used to play this game back in 2002 in Windows XP and I never won this game, I never even understood how this game works until today when I read how it really works 😀

In few minutes my notifications were flooded, I didn’t expect to get this much of likes. Some people asked me a tutorial on this. I thought of writing a very quick blog post on this. Pardon me if I missed anything.
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