hacktricks/reversing/common-api-used-in-malware.md

# Common API used in Malware

## Generic

### Networking

| Raw Sockets   | WinAPI Sockets |
| ------------- | -------------- |
| socket()      | WSAStratup()   |
| bind()        | bind()         |
| listen()      | listen()       |
| accept()      | accept()       |
| connect()     | connect()      |
| read()/recv() | recv()         |
| write()       | send()         |
| shutdown()    | WSACleanup()   |

### Persistence

| Registry         | File          | Service                      |
| ---------------- | ------------- | ---------------------------- |
| RegCreateKeyEx() | GetTempPath() | OpenSCManager                |
| RegOpenKeyEx()   | CopyFile()    | CreateService()              |
| RegSetValueEx()  | CreateFile()  | StartServiceCtrlDispatcher() |
| RegDeleteKeyEx() | WriteFile()   |                              |
| RegGetValue()    | ReadFile()    |                              |

### Encryption

| Name                  |
| --------------------- |
| WinCrypt              |
| CryptAcquireContext() |
| CryptGenKey()         |
| CryptDeriveKey()      |
| CryptDecrypt()        |
| CryptReleaseContext() |

### Anti-Analysis/VM

| Function Name                                             | Assembly Instructions |
| --------------------------------------------------------- | --------------------- |
| IsDebuggerPresent()                                       | CPUID()               |
| GetSystemInfo()                                           | IN()                  |
| GlobalMemoryStatusEx()                                    |                       |
| GetVersion()                                              |                       |
| CreateToolhelp32Snapshot \[Check if a process is running] |                       |
| CreateFileW/A \[Check if a file exist]                    |                       |

### Stealth

| Name                     |                                                                            |
| ------------------------ | -------------------------------------------------------------------------- |
| VirtualAlloc             | Alloc memory (packers)                                                     |
| VirtualProtect           | Change memory permission (packer giving execution permission to a section) |
| ReadProcessMemory        | Injection into external processes                                          |
| WriteProcessMemoryA/W    | Injection into external processes                                          |
| NtWriteVirtualMemory     |                                                                            |
| CreateRemoteThread       | DLL/Process injection...                                                   |
| NtUnmapViewOfSection     |                                                                            |
| QueueUserAPC             |                                                                            |
| CreateProcessInternalA/W |                                                                            |

### Execution

| Function Name    |
| ---------------- |
| CreateProcessA/W |
| ShellExecute     |
| WinExec          |
| ResumeThread     |
| NtResumeThread   |

### Miscellaneous

* GetAsyncKeyState() -- Key logging
* SetWindowsHookEx -- Key logging
* GetForeGroundWindow -- Get running window name (or the website from a browser)
* LoadLibrary() -- Import library
* GetProcAddress() -- Import library
* CreateToolhelp32Snapshot() -- List running processes
* GetDC() -- Screenshot
* BitBlt() -- Screenshot
* InternetOpen(), InternetOpenUrl(), InternetReadFile(), InternetWriteFile() -- Access the Internet
* FindResource(), LoadResource(), LockResource() -- Access resources of the executable

## Malware Techniques

### DLL Injection

Execute an arbitrary DLL inside another process

1. Locate the process to inject the malicious DLL: CreateToolhelp32Snapshot, Process32First, Process32Next
2. Open the process: GetModuleHandle, GetProcAddress, OpenProcess
3. Write the path to the DLL inside the process: VirtualAllocEx, WriteProcessMemory
4. Create a thread in the process that will load the malicious DLL: CreateRemoteThread, LoadLibrary

Other functions to use: NTCreateThreadEx, RtlCreateUserThread

### Reflective DLL Injection

Load a malicious DLL without calling normal Windows API calls.\
The DLL is mapped inside a process, it will resolve the import addresses, fix the relocations and call the DllMain function.

### Thread Hijacking

Find a thread from a process and make it load a malicious DLL

1. Find a target thread: CreateToolhelp32Snapshot, Thread32First, Thread32Next
2. Open the thread: OpenThread
3. Suspend the thread: SuspendThread
4. Write the path to the malicious DLL inside the victim process: VirtualAllocEx, WriteProcessMemory
5. Resume the thread loading the library: ResumeThread

### PE Injection

Portable Execution Injection: The executable will be written in the memory of the victim process and it will be executed from there.

### Process Hollowing

The malware will unmap the legitimate code from memory of the process and load a malicious binary

1. Create a new process: CreateProcess
2. Unmap the memory: ZwUnmapViewOfSection, NtUnmapViewOfSection
3. Write the malicious binary in the process memory: VirtualAllocEc, WriteProcessMemory
4. Set the entrypoint and execute: SetThreadContext, ResumeThread

## Hooking

* The **SSDT** (**System Service Descriptor Table**) points to kernel functions (ntoskrnl.exe) or GUI driver (win32k.sys) so user processes can call these functions.
  * A rootkit may modify these pointer to addresses that he controls
* **IRP** (**I/O Request Packets**) transmit pieces of data from one component to another. Almost everything in the kernel uses IRPs and each device object has its own function table that can be hooked: DKOM (Direct Kernel Object Manipulation)
* The **IAT** (**Import Address Table**) is useful to resolve dependencies. It's possible to hook this table in order to hijack the code that will be called.
* **EAT** (**Export Address Table**) Hooks. This hooks can be done from **userland**. The goal is to hook exported functions by DLLs.
* **Inline Hooks**: This type are difficult to achieve. This involve modifying the code of the functions itself. Maybe by putting a jump at the begging of this.