The story of the macOS High Sierra 10.13.1 DMG is one of refinement, a critical security "oops," and its lasting legacy as the end of the road for many classic Macs.
Terminal Command: On a compatible Mac, you can attempt to download the full installer using this command:softwareupdate --fetch-full-installer --full-installer-version 10.13.6Note: 10.13.6 is the final version; 10.13.1 is generally no longer hosted individually on Apple's primary update servers. Alternative "DMG" Retrieval macos high sierra 10131 dmg
Official App Store: The latest version of High Sierra (10.13.6) can still be accessed via a direct App Store link using Safari on compatible Macs. Key Features & Fixes in 10.13.1 The story of the macOS High Sierra 10
The only safe sources are: