CVE-2024-11166: TCAS II Transponder DoS Vulnerability

CVE-2024-11166 Overview

CVE-2024-11166 is a protocol vulnerability affecting Traffic Collision Avoidance System II (TCAS II) implementations that use transponders compliant with Minimum Operational Performance Standards (MOPS) earlier than RTCA DO-181F. The vulnerability allows an attacker within adjacent network range to impersonate a ground station and issue a Comm-A Identity Request. This malicious action can manipulate the Sensitivity Level Control (SLC) to its lowest setting and disable the Resolution Advisory (RA) functionality, effectively creating a denial-of-service condition that compromises aircraft collision avoidance capabilities.

Critical Impact

Exploitation of this vulnerability can disable critical aircraft collision avoidance systems, potentially leading to dangerous flight conditions where pilots receive no resolution advisories during potential mid-air collision scenarios.

Affected Products

• TCAS II systems using transponders compliant with MOPS earlier than RTCA DO-181F
• Legacy aviation transponder equipment without DO-181F compliance
• Aircraft collision avoidance systems with vulnerable transponder configurations

Discovery Timeline

• 2025-01-22 - CVE CVE-2024-11166 published to NVD
• 2025-01-22 - Last updated in NVD database

Technical Details for CVE-2024-11166

Vulnerability Analysis

This vulnerability is classified under CWE-15 (External Control of System or Configuration Setting), which describes scenarios where an external party can manipulate system configurations without proper authorization. The attack requires adjacent network access, meaning an attacker must be within radio frequency range to transmit signals that impersonate legitimate ground station communications.

The fundamental security weakness lies in the authentication mechanisms (or lack thereof) within the legacy MOPS standards. Transponders compliant with versions prior to RTCA DO-181F do not adequately verify the authenticity of ground station identity requests, allowing forged Comm-A Identity Requests to be processed as legitimate commands.

Root Cause

The root cause stems from insufficient authentication and validation of ground station communications in legacy TCAS II transponder specifications. The MOPS versions predating RTCA DO-181F were designed in an era with different threat assumptions and did not incorporate robust cryptographic verification or source authentication for incoming control messages. This design oversight enables attackers to craft and transmit spoofed ground station signals that the transponder accepts and processes without verification.

Attack Vector

The attack exploits the adjacent network attack vector through radio frequency transmission. An attacker positioned within RF range of the target aircraft can broadcast a malicious Comm-A Identity Request that mimics legitimate ground station traffic. Upon receiving this spoofed request, the vulnerable transponder:

1. Processes the request without authenticating the source
2. Adjusts the Sensitivity Level Control (SLC) to minimum levels
3. Disables the Resolution Advisory (RA) functionality
4. Enters a degraded operational state where collision warnings are suppressed

This attack does not require user interaction or any privileges on the target system, making it particularly concerning for aviation safety. The vulnerability primarily impacts availability and integrity of the collision avoidance system while not directly exposing confidential data.

Detection Methods for CVE-2024-11166

Indicators of Compromise

• Unexpected changes to TCAS II Sensitivity Level Control settings during flight
• Resolution Advisory functionality disabled without pilot intervention
• Anomalous Comm-A Identity Requests logged by aircraft systems
• Sudden degradation of TCAS II functionality without corresponding maintenance events

Detection Strategies

• Implement RF monitoring solutions to detect unusual ground station impersonation patterns in proximity to aircraft
• Review TCAS II system logs for unauthorized configuration changes to SLC settings
• Deploy anomaly detection for unexpected RA disablement events during flight operations
• Cross-reference ground station communications with known legitimate transmission sources

Monitoring Recommendations

• Establish baseline TCAS II operational parameters and alert on deviations
• Implement continuous monitoring of transponder configuration state changes
• Coordinate with air traffic control to verify legitimate ground station communications
• Document and investigate any unexplained TCAS II performance degradation

How to Mitigate CVE-2024-11166

Immediate Actions Required

• Inventory all aircraft systems using TCAS II transponders to identify those with pre-DO-181F compliance
• Review the CISA ICS Advisory ICSA-25-021-01 for detailed mitigation guidance
• Coordinate with aircraft manufacturers and transponder vendors regarding upgrade paths
• Implement enhanced crew procedures for manual collision avoidance awareness when TCAS II anomalies are detected

Patch Information

Organizations should consult the official CISA ICS Advisory ICSA-25-021-01 for authoritative guidance on available patches and firmware updates. Upgrading transponders to comply with RTCA DO-181F or later standards is the recommended long-term remediation, as these newer specifications incorporate improved security controls to address this vulnerability class.

Workarounds

• Enhance pilot situational awareness training regarding potential TCAS II degradation scenarios
• Implement redundant collision avoidance procedures that do not solely rely on TCAS II RA functionality
• Consider RF shielding or filtering solutions where operationally feasible to reduce exposure to spoofed signals
• Coordinate with air traffic control for enhanced separation services when operating aircraft with known vulnerable transponders