There are 215,000 cell phone towers in the U.S. alone, collectively providing coverage to mobile devices around the country. With 2.6 billion smartphone users worldwide, imagine the amount of data transmitted between those towers.
This massive amount of information makes these towers prime targets for cybercriminals. New research has found specific vulnerabilities that target base transceiver stations (BTS), the technical term used to describe cellular towers through which smartphones connect to wireless communications networks, including GSM, UMTS and LTE.
The structure of BTS products makes these vulnerabilities especially concerning. The stations are composed of software and radio equipment equivalent to wireless access points for Wi-Fi networks. The most commonly available BTS software shares the same transceiver code base, regardless if the products are GSM, UMTS, or LTE, since the transceiver is the standalone component. That means all networks are affected by the same vulnerabilities, and the phone calls, SMS messages and data packets that run through them are at risk.
In particular, there are three vulnerabilities found in widely used software running on BTS — vulnerabilities that could allow a remote control takeover, GSM traffic hijacking, various information disclosure, DoS, or worse. Here’s the breakdown:
- Overly Exposed Service Binding: An overly exposed service binding vulnerability allows any attacker with IP connectivity to the BTS system to receive and send data packets to and from the transceiver via the Internet. A hacker with connectivity can then send a User Data Protocol (UDP) — basically a packet of information — to exercise any functionality provided, including SMS messages, transmit calls and data packets from phones to the mobile operator’s data center. Moreover, the attacker can access remote control of a BTS station, remove information from the passing data, make changes to the GSM traffic or completely crash the BTS station.
- Remote Stack-Based Buffer Overflow: An attacker can overflow a stack buffer by sending an oversized UDP packet to the control channel. By exploiting this bug, the attacker can achieve remote code execution (RCE), which allows a hacker to access someone else’s computing device and make changes, regardless of the device’s location. A cybercriminal could also cause a denial of service (DoS) condition, which can make a machine or network resource unavailable to its intended users, indefinitely interrupting or suspending the services of a host connected to the Internet.
- Remote Unauthenticated Control: The control channel of a BTS station doesn’t implement any type of authentication. For this reason, it’s exposed to the outer network due to the overly exposed service binding, as explained in the first vulnerability. Consequently, it can be used by any malicious party to control the transceiver module remotely, meaning an attacker could deny service by turning the module off, jam frequencies by turning the TEX radio to the wrong frequency or hijack a BTS station’s identity, remotely using the SETBSIC command to change the BTS identity to another one.
Just as we secure our smartphones from hackers stealing critical information, we need to secure the whole cellular network by mitigating the potentials risks cell phone towers pose. In order to make their products safer, carriers and vendors should apply the following mitigations:
- Update BTS software whenever a patch is available
- Bind the sockets used for control and data exchange only to the local interface
- Block traffic coming from external networks to the control and data port or other ports used by BTS software
- Apply compile time mitigations
- Implement an authentication system for such channels to deny an unprivileged attacker logged on the same machine, or on the same network, from communicating with BTS control ports
- Fix buffer handling by using correct sizes; perform extra code audits.
The possible implications of BTS vulnerabilities are similar to those resulting from other types of attacks on corporate or BYOD devices, which are often a gateway for malicious attacks on a corporate network. To fully protect sensitive, corporate data, security and mobility professionals must consider an on-device solution to detect any active manipulation by an unauthorized third party.
While the majority of these devices are not publicly accessible and can only be accessed through the carrier’s internal network, there are still many at risk. For a deeper analysis of each BTS vulnerability, please refer to my latest blog post.
Filed Under: Infrastructure
