I had this update hang-up on a new HP laptop with Win8 pre-installed. I found lots of suggestions on several forums, most focused on video or sound card drivers. I tried everything to no avail. I had narrowed it down to KB2756872 by successfully installing all other updates offered in MS Update. Then after the last attempt to install KB2756872, it disappeared from the list in MS Update. I thought, good riddance, I am tired of fooling with it anyway, Microsoft should fix it.

Then KB2770917 appeared in MS Update, and it produced the same hang-up at 12 or 13%. The same as with KB2756872, it would attempt 3 reboots before deciding to revert the changes. I did not try again, thinking Microsoft should fix the problem.

Maybe they have. When KB2771431 appeared in MS Update, I read the "more information" page linked to from MS Update. It does not mention that it corrects any specific previous updates, but the info led me to believe (hope) that it would correct the "12% hang-up".

Bottom Line, what worked for me:
Install KB2771431
Install KB2770917
KB2756872 reappeared in MS Update
Install KB2756872

When done in that order, all went without a hitch. I am hoping this info will help others who have been frustrated with this problem.