The information you seek is not readily available, as a variable, to a custom static widget.
If you were interested, you would have to:
Edit "packages/vbcms/widgets/recentthreads.php" Line: 464
Alter the query there to include attachments.
Make it available to your custom widget template.
I know this is not what you are looking for, but all I have time to do is point you in the right direction.
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