Q: Given the following code slice:
```
1 static BOOL rdp_redirection_read_base64_wchar(UINT32 flag, wStream* s, UINT32* pLength,
6 	const BYTE* ptr = NULL;
8 	if (!rdp_redirection_get_data(s, pLength, &ptr))
10 	const WCHAR* wchar = (const WCHAR*)ptr;
13 	char* utf8 = ConvertWCharNToUtf8Alloc(wchar, *pLength, &utf8_len);```
which has a CWE-787 vulnerability at line:
```
13 	char* utf8 = ConvertWCharNToUtf8Alloc(wchar, *pLength, &utf8_len);
```
Please analyze the root cause of the vulnerability.