Breaking LTE on Layer Two

Abstract

Long Term Evolution (LTE) is the latest mobile communication standard and has a pivotal role in our information society: LTE combines performance goals with modern security mechanisms and serves casual use cases as well as critical infrastructure and public safety communications. Both scenarios are demanding towards a resilient and secure specification and implementation of LTE, as outages and open attack vectors potentially lead to severe risks. Previous work on LTE protocol security identified crucial attack vectors for both the physical (layer one) and network (layer three) layers. Data link layer (layer two) protocols, however, remain a blind spot in existing LTE security research.In this paper, we present a comprehensive layer two security analysis and identify three attack vectors. These attacks impair the confidentiality and/or privacy of LTE communication. More specifically, we first present a passive identity mapping attack that matches volatile radio identities to longer lasting network identities, enabling us to identify users within a cell and serving as a stepping stone for follow-up attacks. Second, we demonstrate how a passive attacker can abuse the resource allocation as a side channel to perform website fingerprinting that enables the attacker to learn the websites a user accessed. Finally, we present the ALTER attack that exploits the fact that LTE user data is encrypted in counter mode (AES-CTR) but not integrity protected, which allows us to modify the message payload. As a proof-of-concept demonstration, we show how an active attacker can redirect DNS requests and then perform a DNS spoofing attack. As a result, the user is redirected to a malicious website. Our experimental analysis demonstrates the real-world applicability of all three attacks and emphasizes the threat of open attack vectors on LTE layer two protocols.

Privacy Attacks to the 4G and 5G Cellular Paging Protocols Using Side Channel Information

“…In contrast, our ToRPEDO exploits the protocol standard's vulnerability of choosing fixed paging frames for a subscriber which makes all the network operators vulnerable to this attack. Rupprecht et al [31] and Jover et al [32] demonstrated that an adversary can identify victim UE's short-lived, lower-layer identifier (C-RNTI) when given the UE's TMSI and thus track the victim's UE. ToRPEDO, on the contrary, recovers the UE's PFI (and TMSI as a side effect) which enables tracking victim's UE irrespective of short-lived C-RNTIs or TMSIs.…”

Towards Resilient 5G: Lessons Learned from Experimental Evaluations of LTE Uplink Jamming

“…In LTE, this task is facilitated by the lack of Media Access Control (MAC) and Radio Link Control (RLC) encryption. Thus, subscribers may be de-anonymized [2] or User Equipment (UE) locations can be tracked [3]. In case of stationary UEs, e.g.…”

Security and Protocol Exploit Analysis of the 5G Specifications

“…The existence of LTE protocol vulnerabilities has been known for some time, although these have not been publicly discussed until recently. The openness of the standard, the large community of researchers, and the broad availability of SDRs, software libraries and open-source implementations of both the eNodeB and the UE protocol stacks have enabled a number of excellent LTE security analyses [5], [9], [10], [28], [29]. Despite the stronger cryptographic algorithms and mutual authentication, UEs and base stations exchange a substantial amount of pre-authentication messages that can be exploited to launch denial of service (DoS) attacks [6], [14], [30], catch IMSIs [31] or downgrade the connection to an insecure GSM link [7], [10].…”

“…Nevertheless, a series of vulnerabilities inherent to the LTE protocol still exist and have been identified by researchers over the last few years. For example, a substantial number of pre-authentication messages are sent in the clear, which can be exploited to launch Denial of Service (DoS) attacks and obtain location information of mobile subscribers [5]- [7].…”

“…LTE opensource software libraries running on personal computers and using commercial off-the-shelf software-defined radio (SDR) peripherals did not reach a sufficient level of maturity until recent years. Once they became available, a wave of excellent security research in the area of LTE mobile communications emerged and identified numerous protocol vulnerabilities [5], [7]- [10].…”