Security

Internet recoveryOS and diagnostics environments in Mac computers

If an error has occurred in the launching of the local recovery or diagnostic environments, the UEFI firmware attempts to download the images from the Internet instead. Additionally, a user can request that the images be fetched from the Internet using special key sequences held at boot. The integrity validation of the disk images and chunklists downloaded from the OS Recovery Server is performed the same way as with images retrieved from a storage device.

While the connection to the OS Recovery Server is done using HTTP, the complete downloaded contents are still integrity checked as previously described, and as such are not vulnerable to manipulation by an attacker with control of the network. In the event that an individual chunk fails integrity verification, it’s requested again from the OS Recovery Server 11 times, before giving up and displaying an error.

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Apple Platform Security

Internet recoveryOS and diagnostics environments in Mac computers