MFA bombing taken to the next level

Simply put, MFA bombing (also known as “push bombing” or “MFA fatigue”) is a brute force attack on your patience. Cybercriminals use MFA bombing to break into accounts that are protected by multi-factor authentication (MFA).

MFA normally requires a user to enter a six-digit code sent by SMS, or generated by an app, or to respond to a push notification, when they enter a username and password. It provides an enormous increase in security and makes life much harder for criminals.

Because it’s so hard to break, criminals have taken to getting users to defeat their own MFA. They do this by using stolen credentials to try logging in, or by trying to reset a user’s password over and over again. In both cases this bombards the user with push notifications asking them to approve the login, or messages asking them to change their password. By doing this, the criminals hope that users will either tap the wrong option or get so fed up they just do whatever the messages are asking them to do, just to make the bombardment stop.

Now, according to this blog by Bran Krebs, these attacks have evolved. If you can withstand the pressure of the constant notifications, the criminals will call you pretending to come to your rescue.

In one example Krebs writes about, criminals flooded a target’s phone with password reset notifications for their Apple ID. Each notification required the user to choose either “Allow” or “Don’t Allow” before they could go back to using their device.

After withstanding the temptation to click “Allow”, and declining “100-plus” notifications, the victim receved a call from a spoofed number pretending to be Apple Support.

The call was designed to get the victim to trigger a password reset, and then to hand over the one-time password reset code sent to their device. Armed with a reset code, the criminals could change the victim’s password and lock them out of their account.

Luckily, in this situation the victim thought the callers seemed untrustworthy, so he asked them to provide some of his personal information, and they got his name wrong.

Another victim of MFA bombing learned that the notifications kept coming even after he bought a new device and created a new Apple iCloud account. This revealed that the attacks must have been targeted at his telephone number, because it was the only constant factor between the two device configurations.

Yet another target was told by Apple that setting up an Apple Recovery Key for his account would stop the notifications once and for all, although both Krebs and the victim dispute this.

Unfortunately, there doesn’t seem to be a lot you can do once an MFA bombing attack starts other than be patient, and be careful not to click Allow. If you get a call, know that Apple Support will never call you out of the blue, so don’t trust the caller, no matter how convenient their timing.

If you lose control of your Apple ID, go to iforgot.apple.com to start the account recovery process.

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