CreateRemoteThreadEx function (processthreadsapi.h)

Article
11/01/2022

Creates a thread that runs in the virtual address space of another process and optionally specifies extended attributes such as processor group affinity.

Syntax

HANDLE CreateRemoteThreadEx(
  [in]            HANDLE                       hProcess,
  [in, optional]  LPSECURITY_ATTRIBUTES        lpThreadAttributes,
  [in]            SIZE_T                       dwStackSize,
  [in]            LPTHREAD_START_ROUTINE       lpStartAddress,
  [in, optional]  LPVOID                       lpParameter,
  [in]            DWORD                        dwCreationFlags,
  [in, optional]  LPPROC_THREAD_ATTRIBUTE_LIST lpAttributeList,
  [out, optional] LPDWORD                      lpThreadId
);

Parameters

[in] hProcess

A handle to the process in which the thread is to be created. The handle must have the PROCESS_CREATE_THREAD, PROCESS_QUERY_INFORMATION, PROCESS_VM_OPERATION, PROCESS_VM_WRITE, and PROCESS_VM_READ access rights. In Windows 10, version 1607, your code must obtain these access rights for the new handle. However, starting in Windows 10, version 1703, if the new handle is entitled to these access rights, the system obtains them for you. For more information, see Process Security and Access Rights.

[in, optional] lpThreadAttributes

A pointer to a SECURITY_ATTRIBUTES structure that specifies a security descriptor for the new thread and determines whether child processes can inherit the returned handle. If lpThreadAttributes is NULL, the thread gets a default security descriptor and the handle cannot be inherited. The access control lists (ACL) in the default security descriptor for a thread come from the primary token of the creator.

[in] dwStackSize

The initial size of the stack, in bytes. The system rounds this value to the nearest page. If this parameter is 0 (zero), the new thread uses the default size for the executable. For more information, see Thread Stack Size.

[in] lpStartAddress

A pointer to the application-defined function of type LPTHREAD_START_ROUTINE to be executed by the thread and represents the starting address of the thread in the remote process. The function must exist in the remote process. For more information, see ThreadProc.

[in, optional] lpParameter

A pointer to a variable to be passed to the thread function pointed to by lpStartAddress. This parameter can be NULL.

[in] dwCreationFlags

The flags that control the creation of the thread.

Value	Meaning
0	The thread runs immediately after creation.
CREATE_SUSPENDED 0x00000004	The thread is created in a suspended state and does not run until the ResumeThread function is called.
STACK_SIZE_PARAM_IS_A_RESERVATION 0x00010000	The dwStackSize parameter specifies the initial reserve size of the stack. If this flag is not specified, dwStackSize specifies the commit size.

[in, optional] lpAttributeList

An attribute list that contains additional parameters for the new thread. This list is created by the InitializeProcThreadAttributeList function.

[out, optional] lpThreadId

A pointer to a variable that receives the thread identifier.

If this parameter is NULL, the thread identifier is not returned.

Return value

If the function succeeds, the return value is a handle to the new thread.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks

The CreateRemoteThreadEx function causes a new thread of execution to begin in the address space of the specified process. The thread has access to all objects that the process opens. The lpAttribute parameter can be used to specify extended attributes such as processor group affinity for the new thread. If lpAttribute is NULL, the function's behavior is the same as CreateRemoteThread.

Prior to Windows 8, Terminal Services isolates each terminal session by design. Therefore, CreateRemoteThread fails if the target process is in a different session than the calling process.

The new thread handle is created with full access to the new thread. If a security descriptor is not provided, the handle may be used in any function that requires a thread object handle. When a security descriptor is provided, an access check is performed on all subsequent uses of the handle before access is granted. If the access check denies access, the requesting process cannot use the handle to gain access to the thread.

If the thread is created in a runnable state (that is, if the CREATE_SUSPENDED flag is not used), the thread can start running before CreateThread returns and, in particular, before the caller receives the handle and identifier of the created thread.

The thread is created with a thread priority of THREAD_PRIORITY_NORMAL. To get and set the priority value of a thread, use the GetThreadPriority and SetThreadPriority functions.

When a thread terminates, the thread object attains a signaled state, which satisfies the threads that are waiting for the object.

The thread object remains in the system until the thread has terminated and all handles to it are closed through a call to CloseHandle.

The ExitProcess, ExitThread, CreateThread, CreateRemoteThread functions, and a process that is starting (as the result of a CreateProcess call) are serialized between each other within a process. Only one of these events occurs in an address space at a time. This means the following restrictions hold:

During process startup and DLL initialization routines, new threads can be created, but they do not begin execution until DLL initialization is done for the process.
Only one thread in a process can be in a DLL initialization or detach routine at a time.
ExitProcess returns after all threads have completed their DLL initialization or detach routines.

A common use of this function is to inject a thread into a process that is being debugged to issue a break. However, this use is not recommended, because the extra thread is confusing to the person debugging the application and there are several side effects to using this technique:

It converts single-threaded applications into multithreaded applications.
It changes the timing and memory layout of the process.
It results in a call to the entry point of each DLL in the process.

Another common use of this function is to inject a thread into a process to query heap or other process information. This can cause the same side effects mentioned in the previous paragraph. Also, the application can deadlock if the thread attempts to obtain ownership of locks that another thread is using.

Requirements

Requirement	Value
Minimum supported client	Windows 7 [desktop apps only]
Minimum supported server	Windows Server 2008 R2 [desktop apps only]
Target Platform	Windows
Header	processthreadsapi.h (include Windows.h on Windows Server 2008 Windows Server 2008 R2)
Library	Kernel32.lib
DLL	Kernel32.dll