I was about to say something like, "Well, in a broad sense they introduced protection features to x86 to prevent modification or disclosure of memory contents across process boundaries...and that's broken, therefore bug."
However, looking at the reference manual for the 80386 [1], and a modern version of their x64 manual [2], they don't actually say it's for security:
Original: "6.1 Why Protection? The purpose of the protection features of the 80386 is to help detect and identify bugs. The 80386 supports sophisticated applications that may consist of hundreds or thousands of program modules..."
Modern: "The IA-32 architecture’s protection mechanism recognizes four privilege levels, numbered from 0 to 3, where a greater number mean less privilege. The reason to use privilege levels is to improve the reliability of operating systems."
So it's more like someone sells you a box with a lock on the front that looks a lot like a safe and all of the individual hinges and pins and whatnot are guaranteed to some degree, but they never actually say it's OK to lock your stuff inside.
[1]https://css.csail.mit.edu/6.858/2013/readings/i386.pdf
[2]https://www.intel.com/content/www/us/en/architecture-and-tec...