BTS (base transceiver station) products are susceptible to complete takeover because of critical vulnerabilities affecting the underlying software, security firm Zimperium warns.
All BTS are comprised of software and radio equipment, and the security company has discovered that most commonly available software shares the same or very similar transceiver code base, which means that all are likely impacted by the same vulnerabilities.
These flaws, the security researchers reveal, could allow a malicious attacker to gain remote control of the transceiver module, which would result in a compromise of the BTS functionalities. Furthermore, the attacker could impersonate a parallel BTS communicating with it and could send GSM data bursts to the transceiver itself, thus conducting attacks such as IMSI detaching, encryption downgrading, and denial of service, among others, against mobile subscribers.
The affected products, researchers say, include YateBTS 5.0.0 and prior, OpenBTS 4.0.0 and prior, OpenBTS-UMTS 1.0.0 and prior, and Osmo-TRX/Osmo-BTS and 0.1.10 prior. Additionally, all other products that share the same transceiver code base are vulnerable, Zimperium says. Affected vendors include Legba Incorporated (YateBTS), Range Networks (OpenBTS and OpenBTS-UMTS), and OsmoCOM (Osmo-TRX and Osmo-BTS).
“There’s a bug in the network library of the aforementioned products which makes the transceiver UDP sockets bind to INADDR_ANY instead of the user configured value (127.0.0.1 by default),” researchers say. “An attacker with IP connectivity could send UDP traffic to exercise any functionality provided. This could allow remote control takeover, GSM traffic hijacking, various information disclosure, DoS, or worse.”
Because of this issue, an attacker with IP connectivity to the BTS system can receive and send packets from/to the transceiver, Zimperium explains. What’s more, there’s no authentication mechanism protecting the access to the services exposed on these UDP network sockets, the security company notes.
Another issue could allow an attacker to overflow a stack buffer by sending an oversized UDP packet to the control channel. By exploiting this bug, an attacker could achieve remote code execution (RCE) or cause a denial of service (DoS) condition. The good news is that the RCE issue can be mitigated when the appropriate flags are applied in compile time. The company also advises blocking this port from external connections on the firewall, if there is no impact on usage of the transceiver interface.
A third issue resides in the lack of authentication in the control channel and is conditioned by the first bug, which exposes it to the outer network, allowing a malicious actor to control the transceiver module remotely. Thus, an attacker could turn the module off to deny service, could tune the TX radio to the wrong frequency to jam frequencies, or could change the BTS identity to another one.
According to Zimperium, it’s the complete lack of any form of authentication, paired with code bugs that turn the aforementioned BTS produtcs vulnerable to a wide range of attacks. To mitigate these issues, vendors are advised to update the BTS software when a patch is available; bind the sockets used for control and data exchange only to the local interface (127.0.0.1); change firewall rules to block traffic coming from external networks to specific ports; implement an authentication system; fix buffer handling by using correct sizes; and perform additional code audits.
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