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I originally posted this on the Apple Stack Exchange but it was suggested that it was off topic, so I’m posting it here in hopes that this is a more relevant place for it.

Say that an iOS device has been compromised by some vulnerability. If one were to backup their device to their computer (or iCloud, but it’s my understanding that making an encrypted backup to a computer allows for more to be stored in the backup, such as passwords) and then restore the OS using the backup to restore settings, could the backup re-compromise the device?

Secondly, have there been any documented cases of persistent threats (outside of jailbreaks) that are remotely exploitable and can persist after a restore?

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    If any of this were possible/known, Apple would be fixing it right away I'd imagine... – multithr3at3d Jul 12 '20 at 2:03
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Theoretically, all off this is possible, but in practice it is rare.

could the backup re-compromise the device?

It could but it probably wouldn't since any malware installed on the device generally wouldn't be backed up. One possible risk would be that if the initial infection occurred through a malicious text/email, and you restore the texts/emails too, then viewing the same text/email might result in reinfection.

have there been any documented cases of persistent threats (outside of jailbreaks) that are remotely exploitable and can persist after a restore?

Yes, for example this proof of concept exploit, which relied on a bug in Broadcom chips, could potentially persist across restores since it overwrote the chip's firmware.

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  • First-hand information? What are your credentials to make the claim that it's extremely rare in practice? Thanks in advance. – 0xC0000022L Jul 12 '20 at 8:50
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    @0xC0000022L It's not really first-hand information. But based on the fact that iPhones are less likely to be infected compared to androids, and that on an updated, non-jailbroken iPhone this would require a zero day exploit (which are potentially worth millions) and combined with multithr3at3d's comment, I believe this is a reasonable claim. – nobody Jul 12 '20 at 9:19
  • @0xC0000022L Although I believe the statistics about higher infection rates for Android devices is due to the fact that there are many, many more outdated and unpatched android devices being used than iPhones – nobody Jul 12 '20 at 9:22

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