The modified phone can block all calls and SMS in the cell

    By making simple changes to a regular Motorola phone, researchers from Berlin were able to block calls and text messages for people in the same location area. Their method works in 2G networks, which are the most common in the world, writes MIT Technology Review.

    The attack consists in modifying the firmware, which can trick the network of delivering incoming calls and SMS. In theory, one phone can block the service for all base station subscribers, says Jean-Pierre Seifert, head of the research group at the Technical University of Berlin. Seyfert and colleagues presented their report at the Usenix Security Symposium in Washington last week. Below you can see a video demonstrating the experiment:



    Seyfert and colleagues changed the firmware of the baseband processor responsible for communicating directly with the transmitting station. In a normal situation, when making a call or SMS, the cell “polls” the connected devices to find the one to which they are intended. And only one phone answers, in fact, saying “It's me,” Seyfert explains. The actual call or message comes to him. The modified firmware can answer any call and do it faster than the victim. During the survey, she will say “It's me”, and the subscriber will never receive a call.

    The research group itself, however, never intercepted calls or SMS in reality, it was able to crack the device polling process and test it on its own numbers. According to assumptions, in their location area to completely turn off the country's third mobile operator E-Plus, only 11 modified phones will be enough. “They will all listen to network requests and answer“ It's me, ”no one will receive either calls or SMS,” says Seyfert. “The response from the operators is illegal,” he continues. “However, the good old days in which you could assume that all phones are reliable and follow the protocol are over.”

    The basis for the work was the firmware leaked several years ago for the baseband processors of individual phones. This allowed scientists to understand how the algorithm works and “improve” it.

    Researcher Young-Ming Park of Virginia Tech notes that although the attack requires some in-depth knowledge, being implemented “it can be repeated by any engineer with access to the necessary hardware and software.”

    It should be noted that although many operators already use 3G and 4G services, second-generation GSM networks remain the most common in the world. About 4 billion people use them for calls, and operators for machine-to-machine applications. You can fix the vulnerability, but this will require changes in the GSM protocol. “Protection is expensive,” said Victor Ball of Microsoft. "I can only assume that mobile operators do not want to invest in it without an immediate threat."

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