I've looked into this a little more, and it appears to me that the CPanel version of XMB has resolved the issues mentioned in the hackers.com article (though not in the same way as suggested by hackers.com).
The headers.php file begins with [b:6027ab375a]$tempcache = &&;[/b:6027ab375a], which seems to resolve the first issue.
The post.php file includes [b:6027ab375a]if (!is_uploaded_file($attach)){die(&file upload failed&

;}[/b:6027ab375a] which seems to resolve the second issue.
HOWEVER, the CPanel installation includes the file [b:6027ab375a]newinstall.php[/b:6027ab375a], which can be easily exploited to delete all of the data, and I suspect this is how my customer's forum was hacked. Anyone using XMB should delete this file.