Supplemental Update for macOS High Sierra 10.13.3: is there more to it?

Apple has today released another Supplemental Update to macOS High Sierra 10.13.3, apparently just to fix a security vulnerability in which crafted Unicode strings can cause memory corruption, and consequent crashing.

This is available through the App Store, or from the following links for standalone updates:

However, Apple’s account of this update appears incomplete: the update for the iMac Pro is 1.5 GB in size, and that for lesser Macs is almost 600 MB. Does it really take that much to fix this issue?

I will report back once I have more information about the contents of this update.


The matching update for iOS, bringing it to 11.2.6, amounts to a mere 30 MB.

That for macOS High Sierra 10.13.3 includes the following items in its Installer Package:

  • updated System Image Utility,
  • updated Setup Assistant, with six updated plug-ins,
  • six updated public frameworks, and nine private frameworks,
  • a complete set of replacement printing support tools for CUPS.

This Supplemental Update therefore appears to include bug fixes to System Image Utility and Setup Assistant, and an updated version of CUPS printing support. It would be very helpful to know what is fixed in those.