https://updates.cdn-apple.com/...
Apple provides an official, free direct download for the via their support website . While the official file is delivered as a .dmg (disk image) rather than a native .iso , it can be used to create a bootable installation drive or converted to an ISO for use in virtual machines. Official Direct Download Link mac os x mountain lion iso direct download
: Offers community-uploaded ISO and DMG versions for legacy software preservation. https://updates
If you downloaded an ISO from a random website and it fails, here are the most common errors: mac os x mountain lion iso direct download
MD5/SHA Checksums: If the download site provides a checksum, compare it against known values for the 10.8 build to ensure the file is authentic.