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A group of researchers at Ruhr-Universität Bochum and NYU Abu Dhabi have discovered a new attack on 4G and 5G mobile networks that can be used to impersonate users.

Called IMP4GT (IMPersonation attacks in 4G NeTworks), the attack demonstrates that the currently used mutual authentication method, where the smartphone and the network verify their identities, is not a reliable security feature in Long Term Evolution (LTE). The authentication is established on the control plane and does not feature integrity protection of the user plane.

By exploiting the missing integrity protection for user data, IMP4GT allows an attacker to impersonate a user towards the network and vice versa. Furthermore, a reflection mechanism of the IP stack mobile operating system can be abused to build an encryption and decryption oracle and inject arbitrary packets and to decrypt packets, the researchers reveal.

In IMP4GT attack, the researchers explain in a whitepaper (PDF), the impersonation can be conducted on either the uplink direction (the attacker poses as the user towards the network, using the victim’s identity to access IP services) or the downlink direction (the attacker establishes a TCP/IP connection to the phone, bypassing the LTE network’s firewalls).

“This attack has far-reaching consequences for providers and users. Providers can no longer assume that an IP connection originates from the user. Billing mechanisms can be triggered by an adversary, causing the exhaustion of data limits, and any access control or the providers’ firewall can be bypassed,” the researchers say.