[Paper Review] RollBack: A New Time-Agnostic Replay Attack Against the Automotive Remote Keyless Entry Systems

Levente Csikor, Hoon Wei Lim+4 more|arXiv (Cornell University)|Sep 14, 2022

Vehicular Ad Hoc Networks (VANETs)16 references4 citations

TL;DR

RollBack is a novel, time-agnostic replay attack that exploits a rollback-like mechanism in automotive Remote Keyless Entry (RKE) systems by replaying previously captured signals, enabling repeated unauthorized access without jamming. Unlike RollJam, it requires only a single signal capture and works indefinitely, with ~70% of tested vehicles—especially Asian makes—found vulnerable.

ABSTRACT

Today's RKE systems implement disposable rolling codes, making every key fob button press unique, effectively preventing simple replay attacks. However, a prior attack called RollJam was proven to break all rolling code-based systems in general. By a careful sequence of signal jamming, capturing, and replaying, an attacker can become aware of the subsequent valid unlock signal that has not been used yet. RollJam, however, requires continuous deployment indefinitely until it is exploited. Otherwise, the captured signals become invalid if the key fob is used again without RollJam in place. We introduce RollBack, a new replay-and-resynchronize attack against most of today's RKE systems. In particular, we show that even though the one-time code becomes invalid in rolling code systems, replaying a few previously captured signals consecutively can trigger a rollback-like mechanism in the RKE system. Put differently, the rolling codes become resynchronized back to a previous code used in the past from where all subsequent yet already used signals work again. Moreover, the victim can still use the key fob without noticing any difference before and after the attack. Unlike RollJam, RollBack does not necessitate jamming at all. Furthermore, it requires signal capturing only once and can be exploited at any time in the future as many times as desired. This time-agnostic property is particularly attractive to attackers, especially in car-sharing/renting scenarios where accessing the key fob is straightforward. However, while RollJam defeats virtually any rolling code-based system, vehicles might have additional anti-theft measures against malfunctioning key fobs, hence against RollBack. Our ongoing analysis (covering Asian vehicle manufacturers for the time being) against different vehicle makes and models has revealed that ~70% of them are vulnerable to RollBack.

Motivation & Objective

• To identify and exploit a previously unknown resynchronization vulnerability in rolling code-based RKE systems that allows replay attacks after initial signal capture.
• To demonstrate that replaying a few previously captured signals can trigger a rollback mechanism, resynchronizing the system to a past code state.
• To show that the attack is time-agnostic and does not require continuous jamming, making it highly practical for car-sharing and rental scenarios.
• To evaluate the real-world impact by analyzing a broad set of vehicle models, particularly from Asian manufacturers.
• To provide actionable countermeasures and a crowdsourced vulnerability database for vehicle owners and manufacturers.

Proposed method

• Capturing a single RKE signal (e.g., unlock or lock command) from a key fob in a prior interaction, even when out of range.
• Replaying the captured signal multiple times in sequence to trigger a resynchronization mechanism in the vehicle’s RKE receiver.
• Exploiting the safety feature that allows acceptance of future codes, but repurposing it to accept previously used, now-invalidated codes.
• Demonstrating that the attack works regardless of the signal’s function (unlock/lock), making it instruction-agnostic.
• Validating the attack across multiple vehicle makes and models, focusing on Asian manufacturers, using controlled signal replay in real-world conditions.
• Proposing a timestamp-based cryptographic solution as a countermeasure, requiring synchronized clocks and digital signatures to prevent replay.

Experimental results

Research questions

• RQ1 Can a replay attack be mounted against rolling code-based RKE systems without requiring continuous jamming or real-time signal capture?
• RQ2 Does replaying previously captured signals trigger a resynchronization mechanism in RKE systems that allows reuse of invalidated codes?
• RQ3 To what extent is the vulnerability present across different vehicle makes and models, particularly in car-sharing and rental environments?
• RQ4 Can the attack be made time-agnostic, allowing repeated exploitation long after the initial signal capture?
• RQ5 What are the practical countermeasures that can prevent such replay-and-resynchronize attacks in real-world deployments?

Key findings

• RollBack enables repeated unauthorized access to vehicles by replaying a single captured signal multiple times, without requiring jamming or real-time access.
• The attack exploits a resynchronization mechanism in RKE systems that allows acceptance of previously used codes when replayed in sequence, effectively rolling back the system to a prior state.
• The vulnerability affects approximately 70% of tested vehicles, primarily from Asian manufacturers, though the impact is expected to be global.
• The attack is instruction-agnostic—any captured signal (unlock or lock) can trigger the rollback effect, increasing its practicality.
• Unlike RollJam, RollBack does not require continuous deployment; captured signals remain valid indefinitely, making it ideal for long-term exploitation in rental or shared-use scenarios.
• A timestamp-based cryptographic solution was proposed as a countermeasure, but it requires clock synchronization and is not yet widely deployed.