diff --git a/Lib/test/clinic.test b/Lib/test/clinic.test
index 9016cffba95ca4..0228d6be03264c 100644
--- a/Lib/test/clinic.test
+++ b/Lib/test/clinic.test
@@ -1803,12 +1803,12 @@ static PyObject *
 test_Py_UNICODE_converter(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    const Py_UNICODE *a;
-    const Py_UNICODE *b;
-    const Py_UNICODE *c;
-    const Py_UNICODE *d;
+    const Py_UNICODE *a = NULL;
+    const Py_UNICODE *b = NULL;
+    const Py_UNICODE *c = NULL;
+    const Py_UNICODE *d = NULL;
     Py_ssize_t d_length;
-    const Py_UNICODE *e;
+    const Py_UNICODE *e = NULL;
     Py_ssize_t e_length;
 
     if (!_PyArg_ParseStack(args, nargs, "O&O&O&u#Z#:test_Py_UNICODE_converter",
@@ -1839,7 +1839,7 @@ test_Py_UNICODE_converter_impl(PyObject *module, const Py_UNICODE *a,
                                const Py_UNICODE *b, const Py_UNICODE *c,
                                const Py_UNICODE *d, Py_ssize_t d_length,
                                const Py_UNICODE *e, Py_ssize_t e_length)
-/*[clinic end generated code: output=45e92604de227552 input=064a3b68ad7f04b0]*/
+/*[clinic end generated code: output=9d41b3a38a0f6f2f input=064a3b68ad7f04b0]*/
 
 
 /*[clinic input]
diff --git a/Misc/NEWS.d/next/Windows/2022-10-02-11-59-23.gh-issue-97728.dIdlPE.rst b/Misc/NEWS.d/next/Windows/2022-10-02-11-59-23.gh-issue-97728.dIdlPE.rst
new file mode 100644
index 00000000000000..2a6a253a52aeef
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2022-10-02-11-59-23.gh-issue-97728.dIdlPE.rst
@@ -0,0 +1,3 @@
+Fix possible crashes caused by the use of uninitialized variables when pass
+invalid arguments in :func:`os.system` on Windows and in Windows-specific
+modules (like ``winreg``).
diff --git a/Modules/clinic/_winapi.c.h b/Modules/clinic/_winapi.c.h
index 87f624f9816de3..118e7bfd29fecf 100644
--- a/Modules/clinic/_winapi.c.h
+++ b/Modules/clinic/_winapi.c.h
@@ -192,7 +192,7 @@ _winapi_CreateFileMapping(PyObject *module, PyObject *const *args, Py_ssize_t na
     DWORD protect;
     DWORD max_size_high;
     DWORD max_size_low;
-    LPCWSTR name;
+    LPCWSTR name = NULL;
     HANDLE _return_value;
 
     if (!_PyArg_ParseStack(args, nargs, "" F_HANDLE "" F_POINTER "kkkO&:CreateFileMapping",
@@ -233,8 +233,8 @@ static PyObject *
 _winapi_CreateJunction(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    LPCWSTR src_path;
-    LPCWSTR dst_path;
+    LPCWSTR src_path = NULL;
+    LPCWSTR dst_path = NULL;
 
     if (!_PyArg_CheckPositional("CreateJunction", nargs, 2, 2)) {
         goto exit;
@@ -394,14 +394,14 @@ static PyObject *
 _winapi_CreateProcess(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    const Py_UNICODE *application_name;
+    const Py_UNICODE *application_name = NULL;
     PyObject *command_line;
     PyObject *proc_attrs;
     PyObject *thread_attrs;
     BOOL inherit_handles;
     DWORD creation_flags;
     PyObject *env_mapping;
-    const Py_UNICODE *current_directory;
+    const Py_UNICODE *current_directory = NULL;
     PyObject *startup_info;
 
     if (!_PyArg_ParseStack(args, nargs, "O&OOOikOO&O:CreateProcess",
@@ -749,7 +749,7 @@ _winapi_OpenFileMapping(PyObject *module, PyObject *const *args, Py_ssize_t narg
     PyObject *return_value = NULL;
     DWORD desired_access;
     BOOL inherit_handle;
-    LPCWSTR name;
+    LPCWSTR name = NULL;
     HANDLE _return_value;
 
     if (!_PyArg_ParseStack(args, nargs, "kiO&:OpenFileMapping",
@@ -1216,4 +1216,4 @@ _winapi__mimetypes_read_windows_registry(PyObject *module, PyObject *const *args
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=dfbccec8f11b7433 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=60b036183b92659e input=a9049054013a1b77]*/
diff --git a/Modules/clinic/overlapped.c.h b/Modules/clinic/overlapped.c.h
index 2861338317497c..2f0520d3df4a2c 100644
--- a/Modules/clinic/overlapped.c.h
+++ b/Modules/clinic/overlapped.c.h
@@ -220,7 +220,7 @@ _overlapped_CreateEvent(PyObject *module, PyObject *const *args, Py_ssize_t narg
     PyObject *EventAttributes;
     BOOL ManualReset;
     BOOL InitialState;
-    const Py_UNICODE *Name;
+    const Py_UNICODE *Name = NULL;
 
     if (!_PyArg_ParseStack(args, nargs, "OiiO&:CreateEvent",
         &EventAttributes, &ManualReset, &InitialState, _PyUnicode_WideCharString_Opt_Converter, &Name)) {
@@ -806,7 +806,7 @@ static PyObject *
 _overlapped_Overlapped_ConnectPipe(OverlappedObject *self, PyObject *arg)
 {
     PyObject *return_value = NULL;
-    const Py_UNICODE *Address;
+    const Py_UNICODE *Address = NULL;
 
     if (!PyUnicode_Check(arg)) {
         _PyArg_BadArgument("ConnectPipe", "argument", "str", arg);
@@ -968,4 +968,4 @@ _overlapped_Overlapped_WSARecvFromInto(OverlappedObject *self, PyObject *const *
 
     return return_value;
 }
-/*[clinic end generated code: output=b0f15f5c09f1147e input=a9049054013a1b77]*/
+/*[clinic end generated code: output=8532bc0e4e1958ac input=a9049054013a1b77]*/
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index ca2699b4e366a3..e636f8b94ff7fe 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -1749,7 +1749,7 @@ os_system(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *k
     static const char * const _keywords[] = {"command", NULL};
     static _PyArg_Parser _parser = {NULL, _keywords, "system", 0};
     PyObject *argsbuf[1];
-    const Py_UNICODE *command;
+    const Py_UNICODE *command = NULL;
     long _return_value;
 
     args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
@@ -9378,4 +9378,4 @@ os_waitstatus_to_exitcode(PyObject *module, PyObject *const *args, Py_ssize_t na
 #ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF
     #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF
 #endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */
-/*[clinic end generated code: output=3032d9c5c3aaa165 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=836be9d51f01140e input=a9049054013a1b77]*/
diff --git a/PC/clinic/_msi.c.h b/PC/clinic/_msi.c.h
index fd21142158312f..b717192b48333a 100644
--- a/PC/clinic/_msi.c.h
+++ b/PC/clinic/_msi.c.h
@@ -195,7 +195,7 @@ _msi_Record_SetString(msiobj *self, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     int field;
-    const Py_UNICODE *value;
+    const Py_UNICODE *value = NULL;
 
     if (!_PyArg_CheckPositional("SetString", nargs, 2, 2)) {
         goto exit;
@@ -244,7 +244,7 @@ _msi_Record_SetStream(msiobj *self, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     int field;
-    const Py_UNICODE *value;
+    const Py_UNICODE *value = NULL;
 
     if (!_PyArg_CheckPositional("SetStream", nargs, 2, 2)) {
         goto exit;
@@ -555,7 +555,7 @@ static PyObject *
 _msi_Database_OpenView(msiobj *self, PyObject *arg)
 {
     PyObject *return_value = NULL;
-    const Py_UNICODE *sql;
+    const Py_UNICODE *sql = NULL;
 
     if (!PyUnicode_Check(arg)) {
         _PyArg_BadArgument("OpenView", "argument", "str", arg);
@@ -650,7 +650,7 @@ static PyObject *
 _msi_OpenDatabase(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    const Py_UNICODE *path;
+    const Py_UNICODE *path = NULL;
     int persist;
 
     if (!_PyArg_CheckPositional("OpenDatabase", nargs, 2, 2)) {
@@ -713,4 +713,4 @@ _msi_CreateRecord(PyObject *module, PyObject *arg)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=d7eb07e6bfcdc13f input=a9049054013a1b77]*/
+/*[clinic end generated code: output=276175d60fbfc956 input=a9049054013a1b77]*/
diff --git a/PC/clinic/winreg.c.h b/PC/clinic/winreg.c.h
index 2507e46e263334..a413dec5dda546 100644
--- a/PC/clinic/winreg.c.h
+++ b/PC/clinic/winreg.c.h
@@ -148,7 +148,7 @@ static PyObject *
 winreg_ConnectRegistry(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    const Py_UNICODE *computer_name;
+    const Py_UNICODE *computer_name = NULL;
     HKEY key;
     HKEY _return_value;
 
@@ -220,7 +220,7 @@ winreg_CreateKey(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
     HKEY _return_value;
 
     if (!_PyArg_CheckPositional("CreateKey", nargs, 2, 2)) {
@@ -301,7 +301,7 @@ winreg_CreateKeyEx(PyObject *module, PyObject *const *args, Py_ssize_t nargs, Py
     static const char * const _keywords[] = {"key", "sub_key", "reserved", "access", NULL};
     static _PyArg_Parser _parser = {"O&O&|ii:CreateKeyEx", _keywords, 0};
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
     int reserved = 0;
     REGSAM access = KEY_WRITE;
     HKEY _return_value;
@@ -354,7 +354,7 @@ winreg_DeleteKey(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
 
     if (!_PyArg_CheckPositional("DeleteKey", nargs, 2, 2)) {
         goto exit;
@@ -428,7 +428,7 @@ winreg_DeleteKeyEx(PyObject *module, PyObject *const *args, Py_ssize_t nargs, Py
     static const char * const _keywords[] = {"key", "sub_key", "access", "reserved", NULL};
     static _PyArg_Parser _parser = {"O&O&|ii:DeleteKeyEx", _keywords, 0};
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
     REGSAM access = KEY_WOW64_64KEY;
     int reserved = 0;
 
@@ -469,7 +469,7 @@ winreg_DeleteValue(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *value;
+    const Py_UNICODE *value = NULL;
 
     if (!_PyArg_CheckPositional("DeleteValue", nargs, 2, 2)) {
         goto exit;
@@ -619,7 +619,7 @@ static PyObject *
 winreg_ExpandEnvironmentStrings(PyObject *module, PyObject *arg)
 {
     PyObject *return_value = NULL;
-    const Py_UNICODE *string;
+    const Py_UNICODE *string = NULL;
 
     if (!PyUnicode_Check(arg)) {
         _PyArg_BadArgument("ExpandEnvironmentStrings", "argument", "str", arg);
@@ -724,8 +724,8 @@ winreg_LoadKey(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *sub_key;
-    const Py_UNICODE *file_name;
+    const Py_UNICODE *sub_key = NULL;
+    const Py_UNICODE *file_name = NULL;
 
     if (!_PyArg_CheckPositional("LoadKey", nargs, 3, 3)) {
         goto exit;
@@ -805,7 +805,7 @@ winreg_OpenKey(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObje
     static const char * const _keywords[] = {"key", "sub_key", "reserved", "access", NULL};
     static _PyArg_Parser _parser = {"O&O&|ii:OpenKey", _keywords, 0};
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
     int reserved = 0;
     REGSAM access = KEY_READ;
     HKEY _return_value;
@@ -862,7 +862,7 @@ winreg_OpenKeyEx(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyOb
     static const char * const _keywords[] = {"key", "sub_key", "reserved", "access", NULL};
     static _PyArg_Parser _parser = {"O&O&|ii:OpenKeyEx", _keywords, 0};
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
     int reserved = 0;
     REGSAM access = KEY_READ;
     HKEY _return_value;
@@ -953,7 +953,7 @@ winreg_QueryValue(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
 
     if (!_PyArg_CheckPositional("QueryValue", nargs, 2, 2)) {
         goto exit;
@@ -1016,7 +1016,7 @@ winreg_QueryValueEx(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *name;
+    const Py_UNICODE *name = NULL;
 
     if (!_PyArg_CheckPositional("QueryValueEx", nargs, 2, 2)) {
         goto exit;
@@ -1084,7 +1084,7 @@ winreg_SaveKey(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *file_name;
+    const Py_UNICODE *file_name = NULL;
 
     if (!_PyArg_CheckPositional("SaveKey", nargs, 2, 2)) {
         goto exit;
@@ -1153,7 +1153,7 @@ winreg_SetValue(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *sub_key;
+    const Py_UNICODE *sub_key = NULL;
     DWORD type;
     PyObject *value_obj;
 
@@ -1228,7 +1228,7 @@ winreg_SetValueEx(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
     HKEY key;
-    const Py_UNICODE *value_name;
+    const Py_UNICODE *value_name = NULL;
     PyObject *reserved;
     DWORD type;
     PyObject *value;
@@ -1349,4 +1349,4 @@ winreg_QueryReflectionKey(PyObject *module, PyObject *arg)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=7ad1db69bc42cab4 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=e83bdaabb4fa2167 input=a9049054013a1b77]*/
diff --git a/Tools/clinic/clinic.py b/Tools/clinic/clinic.py
index cd0446dc4f05d2..97d8d0a9410b63 100755
--- a/Tools/clinic/clinic.py
+++ b/Tools/clinic/clinic.py
@@ -3522,6 +3522,7 @@ def converter_init(self, *, accept={str}, zeroes=False):
                 self.converter = '_PyUnicode_WideCharString_Opt_Converter'
             else:
                 fail("Py_UNICODE_converter: illegal 'accept' argument " + repr(accept))
+        self.c_default = "NULL"
 
     def cleanup(self):
         if not self.length: