Pierluigi Paganini June 15, 2020

Security vulnerabilities in modern communication protocol GTP used by mobile network operators can be exploited by attackers to target 4G/5G users.

Researchers at cybersecurity firm Positive Technologies Security have discovered several vulnerabilities in communication protocol GPRS Tunnelling Protocol (GTP), that is used by mobile network operators (MNOs). Threat actors could exploit these flaws to conduct several malicious activities against 4G/5G users.

GPRS Tunnelling Protocol (GTP) is a group of IP-based communications protocols used to carry general packet radio service (GPRS) within GSM, UMTS and LTE networks.

Attackers could exploit the flaws to intercept user data, impersonate victims, to carry out denial of service (DoS) attacks or conduct fraud.

“The GTP protocol contains a number of vulnerabilities threatening both mobile operators and their clients. As a result, attackers can interfere with network equipment and leave an entire city without communications, impersonate users to access various resources, and use network services at the expense of the operator or subscribers. Every network tested was vulnerable to DoS, impersonation, and fraud.” reads the report published by the experts. “The risk level should be regarded as high: in some cases, an attack can be performed just by using a mobile phone. Faults in the GTP protocol directly impact 5G networks.”

Between 2018 and 2019 the researchers assessed 28 telecom operators in Europe, Asia, Africa, and South America and verifies the presence of the vulnerabilities in the GTP protocol.

GPRS core network and its successor Evolved Packet Core (EPC) are both based on the GTP protocol. 5G networks use EPC as the core network for wireless communications, for this reason, the vulnerabilities discovered by the experts could affect 5G users too.

The most severe issue affecting the protocol flaw is caused by the fact that the protocol does not check the user’s actual location

“Any guest network where the subscriber is currently located can send a set of signaling messages to the subscriber’s home network, so it is difficult to determine whether incoming traffic is legitimate.” continues the report.

The second architectural flaw is related subscriber credentials that
are checked on S-GW (SGSN) equipment by default. Threat actors could exploit the issue to spoof the node that acts as an SGSN (Serving GPRS Support Node).

Attackers could leverage a compromised identifier to use mobile Internet at the legitimate user’s expense and carry out fraud and impersonation,

Attackers can also hijack user session data containing relevant identifiers (e.g., phone number) of a real subscriber and impersonate him to access the Internet.

“These attacks can also be used by a dishonest MNO to create roaming traffic, with the MNO (falsely) charging another operator for non-existent roaming activity of that operator’s subscribers,” states the report.

“On all tested networks, it was possible to use mobile Internet at the expense of both other subscribers and the operator.”

All the networks assessed by the researchers were vulnerable to denial of service against network equipment. Attackers could exploit the issue to launch a DoS attack preventing valid subscribers from connecting to the Internet.

“Mass loss of communication is especially dangerous for 5G networks, because its subscribers are IoT devices such as industrial equipment, Smart Homes, and city infrastructure,” continues the report.

Experts recommend operators to implement whitelist-based IP filtering at the GTP level to mitigate the vulnerabilities.

“To make things better, operators need to look closely at the GTP protocol, ensure filtering at the GTP level, and deploy purpose-made security solutions. Security must be a priority during network design,” the report concluded. “This is truer now than ever before as operators begin to tackle construction of 5G networks.“

Pierluigi Paganini

(SecurityAffairs – hacking, 5G)

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