VirtualAllocEx

VirtualAllocEx is a Windows API function used to allocate memory in the address space of another process. It's part of the Windows memory management functions and is essential for various advanced operations that involve manipulating the memory of other processes.

VirtualAllocEx allocates a region of memory within the virtual address space of a specified process. The calling process (such as an application or a script) must have appropriate access rights to the target process. This function requires the handle to the process in which memory will be allocated, the desired starting address of the allocation (often set to NULL, letting the system choose the address), the size of the area to allocate, the type of memory allocation, and the type of memory protection desired.

In the context of offensive security, such as penetration testing or ethical hacking, VirtualAllocEx can be used in several ways, including DLL Injection and Process Manipulation:

DLL Injection:

  • Allocating Memory for DLL Path: VirtualAllocEx is used to allocate memory in a target process’s address space to store the path of a malicious DLL.
  • Remote Thread Creation: After the path is written into the allocated memory, functions like CreateRemoteThread are used to create a thread in the target process that calls LoadLibrary. LoadLibrary loads the DLL from the specified path, effectively injecting the DLL into the target process.

Process Manipulation:

  • Altering Process Behavior: It can be used to allocate memory in a process for injecting shellcode. This shellcode can then be executed within the context of the target process, altering its behavior or enabling unauthorized actions.

An example of VirtualAllocEx for DLL injection may be:

  1. An attacker gains access to a system and identifies a process they want to inject a DLL into.
  2. The attacker uses VirtualAllocEx to allocate memory in the target process's address space.
  3. The path to the malicious DLL is written into this allocated space.
  4. The attacker then creates a remote thread in the target process that calls LoadLibrary using the address of the memory with the DLL path.
  5. The target process loads the DLL, executing the attacker's code.