We must be careful where we connect our cell phones. If it is already easy to gain access to our devices over the Internet, providing physical access is even worse. For years, experts have been warning about the risks of using public USB devices to charge the cell phone. This is known as juice jacking. Today we are going to talk about an even more dangerous variant: video jacking.

While the USB allows data to be transferred, the HDMI connection allows an image to be duplicated. Through this function, attackers can record the screen of their phone and see everything that is written or touched on it, be it passwords, account numbers, photos, private texts, or emails. If with the USB port it is possible to install malware, with the HDMI connection the risks are even greater.

How video jacking works

In 2011, security expert Brian Krebs showed how it was possible to install malware via the USB port. In 2016, the same analyst showed the dangers of video jacking, an attack via HDMI access. The description of this type of attack is simple. Let’s say a user connects his cell phone to a fake USB charging station. The public cables that are there to charge the phone have been tampered with.

The novelty with HDMI is that instead of opting for data transfer, the ability to duplicate the screen is used. This allows the attacker to see all the keys being pressed, including the unlock PIN. Everything that appears on the mobile screen can be seen by the attacker.

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video jacking

This is a type of attack that affects most cell phones. They do not need to have an HDMI port, as most smartphones today support HDMI connection through the USB-C port via adapters.

When a user connects a USB-C cable to a cell phone it can be simply to charge it, but it can also be to send data or even to send video. If this video is sent without the user’s knowledge, it could be a case of video jacking.

These attacks can occur in airports or shopping malls, where there are usually public charging stations. A priori they should be safe, but through the HDMI connection, it is possible to spy on the connected device.

Avoiding the attack is easy, but you have to be vigilant

A group of researchers at Florida International University have developed a system they call ‘HDMI-watch’, where they analyze the use of the HDMI connection using algorithms and can detect strange uses. If detected, a message is sent to the user to alert him. Not everyone has access to this system, but it is not necessary if we are attentive.

Most cell phones have this function enabled by default, but more and more phones are sending a notification if the HDMI connection is being used. If we are going to charge the mobile in a public place, the easiest way to make sure that everything is in order is to check if a message appears. If it only says that it is charging, a priori everything is fine. If we charge the phone and an HDMI access notification appears, then we should be suspicious.