Intels own guidelines say that DCI should be disabled by default, although on some systems that was not true[1], afaik (would like to be corrected if wrong) this does not impact vast majority of systems. This seems more like a frontdoor that is supposed to be locked tight rather than an backdoor. The bugs that actually enable DCI could be more likely candidates to be considered backdoors.

[1] https://security-center.intel.com/advisory.aspx?intelid=INTE...

But once that front door is open, people will be able to walk around in the house and figure out how to 1) finally disable the thing for good, or 2) find a more universal attack that doesn't use that door.

This link is broken.

They probably removed the languageid parameter, thinking it was optional.

https://security-center.intel.com/advisory.aspx?intelid=INTE...