Instagram Bug Put User Account Details, Phone Numbers at Risk

A now-patched Instagram vulnerability could have exposed users' account data and phone numbers to cyberattackers, parent company Facebook confirmed in a new report from Forbes.

The bug was discovered by an Israeli hacker who goes by the handle @ZHacker13. It could have potentially been used to access user data including names, full phone numbers, and Instagram account numbers and handles – all an attacker needs to narrow their focus on a specific person.

It's the latest in a series of bad news for Facebook, which recently patched an account-takeover flaw in Instagram that would have let an attacker take over any account by resetting its password. Earlier this month, 419 million phone numbers belonging to Facebook users were found publicly accessible in a third-party database left online without password protection.

This particular vulnerability existed in Instagram's contact importer, which, when subject to brute force attacks, could grant an attacker access to the data. An attacker could use an algorithm to verify individual phone numbers to see which are linked to an Instagram account. Exploiting a second process could give them the name and number linked to the phone number, enabled by the Sync Contacts tool that lets users find their contacts on the platform.

In theory, an attacker could leverage a wealth of bots to brute force Instagram's login form and collect legitimate phone numbers, Forbes points out in its report. Instagram caps syncing to three times per day, per account; however, an attacker with enough bots could bypass this limitation. While this bug was difficult to exploit, it was possible for an attacker to build a collection of user data.

"This vulnerability further demonstrates the over-reliance of phone numbers as a strong form of authentication to digital platforms like Instagram," said Zack Allen, director of threat operations at ZeroFox, who in an email called the importance of phone numbers as identifiers on modern Internet platforms "harrowing."

"A database such as the one leaked last week with millions of phone numbers, and a vulnerability like this to tie accounts to phone numbers, sets a dangerous precedent for those vulnerable to SIM swaps," he added.

@ZHacker13 shared his findings with Facebook in early August. Facebook initially responded, saying these types of vulnerabilities, which show a given email address or phone number is linked with a specific account, are "extremely low risk." However, bugs that let an attacker figure out which user ID an email address or phone number is linked to are another story.

After further communication in which the company reportedly expressed little urgency to fix the problem, Facebook told @ZHacker13 this was "a valid issue." It has now addressed the problem; the researcher has tested his exploit and confirmed with Forbes it no longer works. There has not yet been evidence indicating account data was misused as a result of the vulnerability.

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