CVE-2021-46145: Honda Civic 2012 Auth Bypass Vulnerability

CVE-2021-46145 Overview

CVE-2021-46145 is a security vulnerability affecting the keyfob subsystem in Honda Civic 2012 vehicles that allows attackers to perform a replay attack for unlocking the vehicle. The flaw stems from the implementation of a non-expiring rolling code combined with improper counter resynchronization, enabling an adversary within adjacent network range to capture and replay unlock signals to gain unauthorized vehicle access.

Critical Impact

Attackers with radio frequency capture capabilities can intercept keyfob signals and replay them to unlock Honda Civic 2012 vehicles without the owner's knowledge or authorization.

Affected Products

• Honda Civic 2012 vehicles with keyfob entry systems

Discovery Timeline

• 2022-01-06 - CVE-2021-46145 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-46145

Vulnerability Analysis

This vulnerability is classified under CWE-294 (Authentication Bypass by Capture-Replay), which describes weaknesses where authentication mechanisms can be circumvented by capturing authentication data and replaying it to gain access. The keyfob subsystem in affected Honda Civic 2012 vehicles uses a rolling code mechanism intended to prevent replay attacks by generating a new code for each use. However, the implementation contains a critical flaw: the rolling codes do not expire, and the counter resynchronization mechanism can be exploited.

When a legitimate keyfob signal is transmitted, an attacker within radio frequency range can capture this signal. Due to the non-expiring nature of the rolling codes and the flawed counter resynchronization process, the captured signal remains valid and can be replayed at a later time to unlock the vehicle. This fundamentally undermines the security guarantees that rolling code systems are designed to provide.

Root Cause

The root cause of this vulnerability lies in two interconnected design flaws within the keyfob authentication system:

1. Non-expiring rolling codes: The rolling codes generated by the keyfob do not have a time-based expiration mechanism. Once a code is generated, it remains valid indefinitely until used, creating a window of opportunity for capture and replay.

2. Improper counter resynchronization: The counter synchronization mechanism between the keyfob and the vehicle's receiver allows for replay scenarios. When the vehicle receives a valid code, the improper handling of counter synchronization means previously captured codes may still be accepted under certain conditions.

Attack Vector

The attack requires an adversary to be within adjacent network range (specifically, radio frequency range of the keyfob signal). The attacker must:

1. Position themselves within range when a legitimate keyfob unlock command is transmitted
2. Capture the radio frequency signal containing the rolling code
3. Store the captured signal for later replay
4. Replay the captured signal when the vehicle owner is not present to unlock the vehicle

This attack does not require any user interaction and can be performed without special privileges. The attacker needs appropriate radio frequency capture and transmission equipment, such as a software-defined radio (SDR) device.

The vulnerability allows attackers to capture keyfob signals using radio frequency equipment and replay them to unlock vehicles. The attack exploits the non-expiring rolling code mechanism where captured signals remain valid for replay. Technical details and proof-of-concept demonstrations have been documented by security researchers. See the StarV Lab Analysis and Tiger Team Blog Post for detailed technical breakdowns.

Detection Methods for CVE-2021-46145

Indicators of Compromise

• Unexpected vehicle unlocking events when the owner has not used the keyfob
• Discovery of suspicious individuals with radio equipment near the vehicle during keyfob use
• Evidence of vehicle entry without physical damage or visible break-in signs
• Items missing from the vehicle despite locked doors and no signs of forced entry

Detection Strategies

• Monitor for unusual radio frequency activity in the 315 MHz or 433 MHz bands commonly used by automotive keyfobs near your vehicle
• Review vehicle access logs if the vehicle is equipped with telematics systems that record unlock events
• Consider using a Faraday pouch for storing keyfobs to prevent signal capture when not in use

Monitoring Recommendations

• Be vigilant of individuals with electronic devices positioned near your vehicle when using the keyfob
• For fleet operators, implement logging mechanisms to track vehicle access events and correlate with authorized user activity
• Consider aftermarket security systems that provide additional unlock event notifications

How to Mitigate CVE-2021-46145

Immediate Actions Required

• Store keyfobs in a Faraday bag or RF-shielding container when not in use to prevent signal capture
• Avoid using the keyfob in isolated or suspicious locations where attackers may be waiting to capture signals
• Use manual key entry when possible in high-risk environments
• Consider installing an aftermarket alarm system with additional authentication requirements

Patch Information

At the time of publication, no vendor patch or official fix has been released by Honda for this vulnerability. The keyfob system is hardware-based and may not be easily updated through software patches. Vehicle owners should consult with authorized Honda dealerships for any available security updates or hardware replacements.

Workarounds

• Use a steering wheel lock or other physical anti-theft devices as an additional layer of protection
• Install an aftermarket immobilizer system that requires secondary authentication
• Park in well-lit, monitored areas with security cameras to deter potential attackers
• Consider using the physical key for locking and unlocking instead of the remote keyfob in sensitive situations

Vehicle owners concerned about this vulnerability should contact their local Honda dealership to inquire about any available security enhancements or replacement keyfob systems with improved rolling code implementations.