Fixing “application is damaged, can’t be used to install macOS” Error

This error, thrown while trying to install an old macOS version (probably in a VM!) is caused by an expired certificate.

Good news is: this can be fixed, by deleting a file within the installer itself:

  1. Right click on the Installer XXX.dmg
  2. Click over Show Package Contents
  3. Open Contents > Shared Support
  4. Nuke InstallInfo.plist