The root cause of the CWE-190 (Integer Overflow or Wraparound) vulnerability on line 6 is the potential for the calculations `nXDst * dstBytesPerPixel` and `nYDst * nDstStep` to overflow before the addition takes place.  If either of these multiplications, or their sum, results in a value larger than the maximum representable value for a `UINT32`, the result will wrap around, leading to an unexpectedly small value.  This small value would then be used as an index into `pDstData`, potentially accessing memory outside the intended bounds.

Specifically:

* **`nXDst * dstBytesPerPixel`:**  If `nXDst` and `dstBytesPerPixel` are sufficiently large, their product could exceed the maximum value of a `UINT32`.

* **`nYDst * nDstStep`:** Similarly, if `nYDst` and `nDstStep` are large enough, their product could also overflow.

* **Sum of the Products:** Even if the individual products don't overflow, their sum could still exceed `UINT32_MAX`.

This out-of-bounds memory access can lead to various security issues, such as crashes, denial of service, and potentially arbitrary code execution.

The code doesn't perform any checks to ensure that these multiplications and additions don't overflow, leaving it vulnerable to exploitation.
