Researchers Uncover Vulnerabilities in LTE Wireless Protocol

Researchers from the Korea Advanced Institute of Science and Technology Constitution (KAIST) say they have discovered 36 previously undisclosed vulnerabilities in the Long Term Evolution (LTE) protocol used by most mobile carriers.

The flaws were discovered using a semi-automated testing tool named LTEFuzz, which generates and sends test cases to a target network and then classifies problematic behavior by monitoring device-side logs. The results were confirmed against operational LTE networks. 

In a whitepaper (PDF), the researchers explain that their findings were categorized into five types, namely improper handling of unprotected initial procedure, crafted plain requests, messages with invalid integrity protection, replayed messages, and security procedure bypass.

“The impact of the attacks is to either deny LTE services to legitimate users, spoof SMS messages, or eavesdrop/manipulate user data traffic,” the researchers explain. 

Security vulnerabilities have been discovered in the control plane procedures of LTE networks, but the control plane components in LTE remain unexplored, which determined the researchers to investigate potential issues in this area. 

For their testing, the researchers used open-source LTE implementations meant to create concrete security properties and test cases, and also worked with carriers as part of the investigation, to demonstrate the attacks on commercial networks. They eventually uncovered 36 new flaws in design and implementation among the different carriers and device vendors. 

“The purpose of our study was not to identify failures causing crashes or memory leaks. Instead, we focused on finding semantic failures in LTE operations. To this end, we generated all possible test cases that would have been correctly parsed in the receiving entities as the field values are created based on the control plane logs from the operational networks.” the researchers say.  

The testing revealed that the Radio Resource Control (RRC) Connection procedure is neither encrypted nor integrity protected, which could allow an adversary to exploit the messages in this procedure to spoof the contents or deny the connection of the victim device. 

An attacker could send invalid plain requests through an RRC Connection spoofed as the victim device, and the network may accept invalid messages, de-register an existing connection when receiving a message with an invalid MAC, and accept replayed messages. Furthermore, it is possible to bypass the security context of the entire control plane and data plan, the researchers say. 

Possible attacks would target either the network (remote de-registration of the victim device, SMS phishing) or the victim device (an adversary located sufficiently close to the victim device could trigger handover to a rogue LTE network), the researchers say. 

The study discovered issues not only in the LTE networks, but also in baseband chipsets from Qualcomm and HiSilicon. Thus, the researchers say they want to privately release LTEFuzz to the impacted carriers and vendors in the near future. A public release isn’t planned, as the tool can be used maliciously. 

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