a simple but formidable technique

A researcher has just found an amazing security flaw in WhatsApp. His trick allows you to bypass authentication when the victim’s smartphone is in airplane mode or turned off. And so to hack his account!

Application developers and hackers are constantly racing to find possible flaws in APIs: some to fix them, others to exploit them. And, sometimes, the simplest maneuvers are the best. Zuk Avraham, a cybersecurity researcher and mobile systems specialist, revealed on Twitter that he had discovered an easy to implement, yet formidable technique to take control of the application when the victim’s smartphone is off or on. airplane mode – when she goes to bed for example. The key to success” ? His answering machine.

WhatsApp hack: an attack via voicemail

Typically, when a person is sleeping, they turn off their smartphone or put it on airplane mode so that phone calls don’t wake them up. As a result, they are automatically redirected to the messaging vocal. And it is at this moment, when the victim drops his barriers and surrenders to the arms of Morpheus, that the pirate can strike. According to the method discovered by Zuk Avraham, he will dial the number of the person in order to connect to the account WhatsApp of the latter. The platform will therefore send a verification SMS but, as the smartphone is offline, the message will remain pending. The hacker will therefore perform a new test, but this time requesting verification by call. As the phone is still unavailable, the WhatsApp service will leave a voice message on the user’s mailbox containing the identification number. And here is the drama.

Most operators offer a service to consult these voice messages remotely. To access it, you must enter a four-digit secret code. However, in some countries, this code is composed by default of the last four digits of the telephone number. The hacker only has to try his luck and retrieve the WhatsApp ID number to access the account. The scenario is all the more worrying as the platform has been the subject ofa massive leak in November 2022, with the theft of the telephone data of nearly 500 million people, including more than 20 million French people, which have since been put up for sale on the Dark Web. That’s why it’s important to change your default voicemail code and enable two-factor authentication (2FA), especially since when a WhatsApp account is hacked, the recovery process can take days, giving the hacker plenty of time to defraud contacts and/or distribute malware. It only remains to hope that Meta quickly correct this flaw.

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