The CWE-787 vulnerability is an "Out-of-bounds Write" vulnerability. 

In this case, the vulnerability occurs because the loop counter `i` is bounded by `cinfo->num_components`, but the array `cinfo->cur_comp_info` is bounded by `MAX_COMPS_IN_SCAN`. 

If `cinfo->num_components` is greater than `MAX_COMPS_IN_SCAN`, then the loop will attempt to write to an index of `cinfo->cur_comp_info` that is out of bounds, resulting in undefined behavior.

The root cause of this vulnerability is that the code does not properly validate the relationship between `cinfo->num_components` and `MAX_COMPS_IN_SCAN` before writing to the `cinfo->cur_comp_info` array.

To fix this vulnerability, the code should add a check to ensure that `cinfo->num_components` is not greater than `MAX_COMPS_IN_SCAN` before the loop. Here is an example of how the code could be modified to fix the vulnerability:

```c
if (cinfo->num_components > MAX_COMPS_IN_SCAN) {
    // Handle error: num_components exceeds maximum allowed
    // This could involve returning an error code or throwing an exception
}

for (i = 0; i < cinfo->num_components; i++) {
    cinfo->cur_comp_info[i] = NULL;
}
```

Alternatively, the code could use a more dynamic approach to allocate memory for `cinfo->cur_comp_info` based on the value of `cinfo->num_components`, rather than relying on a fixed-size array.