Stealthy SMS Side-Channel Attack Exposed. When you send an SMS, delivery reports let you know if your message reached the recipient.

But here the most interesting thing is that they also have the potential to provide the location of the receiver.

Researchers have revealed that when you receive a silent SMS message, the sender can easily figure out where you are and it’s possible by looking at when you receive the messages.

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The development of this covert SMS side-channel attack involved researchers from multiple colleges working together.

Here below we have mentioned the name researchers along with their colleges:-

• Evangelos Bitsikas from Northeastern University
• Theodor Schnitzler from Research Center Trustworthy Data Science and Security
• Christina Pöpper from New York University Abu Dhabi
• Aanjhan Ranganathan from Northeastern University

SMS Side-Channel Attack

By analyzing the message timing, a sender can guess the receiver’s location in multiple countries with around 96% accuracy.

This attack primarily focuses on exploiting the main vulnerabilities of the GSMA network, which powers SMS technology. Since this side-channel attack targets GSMA, so, most of the cell phone networks worldwide get covered.

Although there are other communication options like 3G and 4G, the researchers selected to study SMS, as it is widely used by the general public for 2G communication.

The researchers noticed that receiving SMS Delivery Reports after getting an SMS message activates a timing attack vulnerability.

The SMS Delivery Reports feature operates in a way that the recipient cannot prevent its misuse because they have no control over it.

The attacker’s ML model will give more accurate location predictions during the attack if they have precise information about their targets’ whereabouts.

By sending multiple SMS messages to the target, the attacker can collect the data.

To make them discreet, they can present them as marketing messages that the target would likely dismiss or deploy silent SMS messages.

When a silent SMS is sent, it appears as an empty message on the target device without triggering any notifications, but it is still acknowledged as received by the device’s SMSC.

The researchers sent sets of 20 silent SMS messages every hour using ADB for three days to various test devices located in:-

• The United States
• The United Arab Emirates
• Seven European nations

Ten different operators were included in this experiment, which aimed to analyze a wide collection of communication technologies and variations based on different generations.

Network Delay Factors

Here below we have mentioned all the network delay factors:-

• UE Processing
• Propagation Delay
• Routing Delay
• Processing Delay

To perform this attack, the attacker only needs to know the victim’s cell phone number.

Although it takes time, an attacker can uncover a new or unknown location of their target by collecting and analyzing the timing patterns of the user.

While in this case, the time interval between sending and receiving an SMS message can be beneficial significantly.

For location classification, the researchers selected the Multilayer Perceptron (MLP), which is a classifier that is accessible in Python’s SKLearn libraries.

Its selection was based on its versatility in parameter tuning and its remarkable performance with large amounts of data.

Even if the entire world were inaccessible, the accuracy of over 90 percent still poses a privacy risk to individuals.

The researchers found that the existing countermeasures against similar attacks do not work for this specific side-channel attack.

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