Root Cause Analysis: The CWE-787 (Out-of-bounds Write) vulnerability exists in the code because the `strncpy` function is used incorrectly at line 7. The third argument to `strncpy` should be the maximum number of characters to copy, but instead, it is passed `sizeof(szFileName) - 5`, which represents the size of the destination buffer `szFileName` minus 5 bytes.

This can lead to a buffer overflow if the length of `pszFileName` is greater than or equal to `sizeof(szFileName) - 5`. In such cases, `strncpy` will write beyond the bounds of the `szFileName` buffer, resulting in an out-of-bounds write vulnerability (CWE-787).

The correct usage of `strncpy` should be:

```c
strncpy(szFileName, pszFileName, sizeof(szFileName) - 1);
szFileName[sizeof(szFileName) - 1] = '\0'; // Ensure null termination
```

This way, `strncpy` will copy at most `sizeof(szFileName) - 1` characters from `pszFileName` into `szFileName`, ensuring that there is always room for the null terminator, and preventing buffer overflows.