Nearly 50m Facebook accounts were compromised by an attack that gave hackers the ability to take over users’ accounts, Facebook revealed on Friday.
The breach was discovered by Facebook engineers on Tuesday 25 September, the company said, and patched on Thursday. Users whose accounts were affected will be notified by Facebook. Those users will be logged out of their accounts and required to log back in.
“I’m glad we found this and fixed the vulnerability,” Mark Zuckerberg said on a conference call with reporters on Friday morning. “But it definitely is an issue that this happened in the first place. I think this underscores the attacks that our community and our services face.”
The security breach is believed to be the largest in Facebook’s history and is particularly severe because the attackers stole “access tokens”, a kind of security key that allows users to stay logged into Facebook over multiple browsing sessions without entering their password every time. Possessing a token allows an attacker to take full control of the victim’s account, including logging into third-party applications that use Facebook Login.
In a post online Guy Rosen, Facebook’s VP or Product Management, said: “On the afternoon of Tuesday, September 25, our engineering team discovered a security issue affecting almost 50 million accounts.
“We’re taking this incredibly seriously and wanted to let everyone know what’s happened and the immediate action we’ve taken to protect people’s security.
“Our investigation is still in its early stages.
“But it’s clear that attackers exploited a vulnerability in Facebook’s code that impacted “View As”, a feature that lets people see what their own profile looks like to someone else.
“This allowed them to steal Facebook access tokens which they could then use to take over people’s accounts.
“Access tokens are the equivalent of digital keys that keep people logged in to Facebook so they don’t need to re-enter their password every time they use the app.”
Rosen added: “This attack exploited the complex interaction of multiple issues in our code. It stemmed from a change we made to our video uploading feature in July 2017, which impacted “View As.”
“The attackers not only needed to find this vulnerability and use it to get an access token, they then had to pivot from that account to others to steal more tokens.
“Since we’ve only just started our investigation, we have yet to determine whether these accounts were misused or any information accessed.
“We also don’t know who’s behind these attacks or where they’re based. We’re working hard to better understand these details — and we will update this post when we have more information, or if the facts change. In addition, if we find more affected accounts, we will immediately reset their access tokens.”
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