Half a billion Android phones could have data recovered and Google accounts compromised thanks to flaws in the default wiping feature, University of Cambridge scientists Laurent Simon and Ross Anderson have claimed.
The gaffe apparently allows tokens for Google and Facebook, among others, to be recovered in 80 per cent of cases. Encryption keys can also be recovered and, with some brute-force, password guessing can allow attackers to access previously wiped data.
Those keys, along with a host of data including SMS, photos, and videos, can be recovered because the factory reset process in Android 4.3 Jellybean and below is flawed, the boffins said in their paper Security Analysis of Android Factory Resets (PDF).
Here's the gist of it:
We estimate that up to 500 million devices may not properly sanitise their data partition where credentials and other sensitive data are stored, and up to 630 million may not properly sanitise the internal SD card where multimedia files are generally saved.
We found we could recover Google credentials on all devices presenting a flawed factory reset. Full-disk encryption has the potential to mitigate the problem, but we found that a flawed factory reset leaves behind enough data for the encryption key to be recovered.
Simon and Anderson tested 21 phones from five vendors, including Samsung, HTC, and Nexus, running Android versions 2.3 to 4.3.
It's not known how many Android versions above 4.3 are affected. Google has been contacted for comment.
The duo said in the work – considered the first comprehensive analysis of Android factory reset functions – that remote wiping features for lost and stolen phones are subject to the same flaws.
Enterprises that sell off used phones that once contained or were linked to systems that store sensitive corporate information should be concerned about the flaws given the option for skilled data thieves to purchase recycled phones and trawl through system partitions.
Thieves could also buy phones on sites such as eBay in a bid to obtain bank account information, should tried and tested bank trojans prove uninspired.
The researchers matched the most likely crimes to each dataset, suggesting images and browsing histories be used for blackmail and credentials be sold off on the criminal hacking underground.
Lists of installed apps could be useful to determine the value of the previous Android user, such as corporate executives as opposed to school kids, while the "phone owner" facility is useful to contact the victim.
Because encrypted systems could be attacked only after the salted key is cracked, this author suggests users may be able to counter the attack by enabling full disk encryption and creating very long complex passwords just before handsets are wiped for sale in a bid to make brute forcing of keys impractical. ®