The hackers who broke into iCloud accounts could have accessed revealing images and data users believed had been deleted weeks or even months in the past, an eagle-eyed Check Point Software researcher has discovered.
Check Point information security strategist Moti Sagey started looking into the issue after reading a Twitter post from actress Mary Winstead that has come to symbolise the bafflement celebrity victims have expressed in the face of an easy-to-use but also inscrutable technology.
Winstead was one of a 100 celebrities who reportedly had her personal images stolen and leaked by the 4Chan collective during the hack.
"Knowing those photos were deleted long ago, I can only imagine the creepy effort that went into this," she wrote in a 31 August message.
But if she deleted the images "long ago" how were hackers able to access them?
Sagey's belief is that far from requiring a "creepy effort", once they were past the login screen the attackers probably exploited an undocumented quirk in the design of the iCloud backup routine when used from an iOS device such as the iPhone or iPad.
Apple doesn't advertise it, but it turns out that iCloud for iOS saves the last three backup revisions for every device, which for anyone who opted into the service during setup (i.e. almost everyone) will happen once per day as long as Wi-Fi is activated and the device is plugged in and charging.
A few users will activate backups manually but many will just 'set and forget' in which case the three backups inside iCloud will correspond to three consecutive days.
However, a smaller group, including those who travel a lot, might not have Wi-Fi activated while also charging as frequently, in which case the three backups inside the system could end up being days, weeks or even many months apart.
They won't know this of course because according to Sagey only the most recent backup appears. He discovered the two hidden backups while using a utility called DR.Fone that aids in iCloud backup recovery. While using the software he noticed that each iOS device had not one but THREE backups visible, holding files he believed to be long gone.
In simple terms, "if I look I will not see that I have these revisions," Sagey told Techworld. "I'm sure the hackers either knew this or just used a tool and discovered it by mistake," he said.
He speculates that having two hidden backups is probably a convenience for Apple in case the primary one corrupts during the transfer or simply as general insurance.
So Apple's design isn't a bad per se but might aid file trawlers when attacking a subset of users who don't back up often. It should already be clear to most users that simply deleting a file from an iOS device does not mean that it's gone from the iCloud too.
In June, controversial Russian utility firm Elcomsoft started offering a utility that can access iCloud backups without knowing their Apple ID - they do have to have physical access to the device.