Zdziarski tested out his theory by beginning a few chat threads, then archiving, clearing, and deleting them, but found that none of the app's deletion methods, even Clear All Chats, "made any difference in how deleted records were preserved." The central flaw appeared to be in the app's SQLite records, which retained the deleted chats in its database that could be accessed by a harmful individual with the right "popular forensics tools."
In his post, Zdziarski mentioned that the problem isn't unique to WhatsApp, and has even gone into detail about "forensic trace leakage" in Messages on iOS and OS X, and ways Apple could address such privacy issues, in a separate blog post. He explained succinctly that short-lived chats between friends and family using these apps are "not ephemeral on disk," which not only could be a cause for concern with users, but could allow law enforcement legal access to thought-to-be-deleted WhatsApp messages thanks to the lack of encrypted communication between WhatsApp and iCloud.
The core issue here is that ephemeral communication is not ephemeral on disk. This is a problem that Apple has struggled with as well, which I’ve explained and made design recommendations recently in this blog post.All the same, Zdziarski caps his post by mentioning there's no reason for widespread panic to ignite because of the WhatsApp security flaw, mainly due to the fact that someone with malicious intent would need to jump through so many hoops to finally access the deleted messages. The iOS researcher stated that his purpose was for users to simply "be aware of WhatsApp’s footprint." He also gives a few options for users looking to mitigate the issue, including periodically deleting WhatsApp "to flush out the database," disabling iCloud backups, and avoiding the storage of backup passwords in Apple's keychain.
Apple’s iMessage has this problem and it’s just as bad, if not worse. Your SMS.db is stored in an iCloud backup, but copies of it also exist on your iPad, your desktop, and anywhere else you receive iMessages. Deleted content also suffers the same fate.
Earlier in the year, Apple reiterated its intent to double down on user privacy and safety within its iCloud platform. Currently, encrypted data saved in iCloud is accessible by Apple with a key, which grants it access to accounts for assistive purposes, like if someone forgets their password. However, with the steadily growing data amassing in users' iCloud accounts -- from texts to pictures and personal health data -- Apple is looking to provide end-to-end encryption in its cloud-based storage platform, meaning not even the company itself could gain access to the accounts of its users even if it wanted to.
Check out Zdziarski's blog post for more details on the issue.