CVE-2021-28136 in ESP-IDF (BrakTooth)
Summary
by MITRE • 09/07/2021
The Bluetooth Classic implementation in Espressif ESP-IDF 4.4 and earlier does not properly handle the reception of multiple LMP IO Capability Request packets during the pairing process, allowing attackers in radio range to trigger memory corruption (and consequently a crash) in ESP32 via a replayed (duplicated) LMP packet.
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Analysis
by VulDB Data Team • 09/10/2021
The vulnerability CVE-2021-28136 represents a critical memory corruption issue within the Bluetooth Classic implementation of Espressif ESP-IDF versions 4.4 and earlier. This flaw specifically targets the pairing process where the system fails to properly handle multiple LMP IO Capability Request packets received simultaneously. The vulnerability exists in the ESP32 wireless microcontroller platform which is widely used in IoT devices and embedded systems, making it particularly concerning for the broader Internet of Things ecosystem. The issue stems from inadequate input validation and packet processing mechanisms within the Bluetooth stack implementation, creating a pathway for remote code execution through carefully crafted malicious packets.
The technical implementation flaw occurs during the Bluetooth pairing phase when multiple LMP IO Capability Request packets are received in rapid succession. The ESP-IDF Bluetooth stack does not properly validate or handle these duplicated packets, leading to memory corruption vulnerabilities that ultimately result in system crashes. This type of vulnerability falls under CWE-129, Input Validation, and CWE-125, Out-of-bounds Read, as the system fails to properly validate incoming packet sequences and processes them without adequate bounds checking. The memory corruption manifests as a buffer overflow or heap corruption during the pairing process, which can be exploited by attackers within radio range to cause denial of service conditions.
From an operational perspective, this vulnerability significantly impacts the security posture of any device utilizing ESP32 chips with affected ESP-IDF versions. The attack requires only proximity to the target device, making it particularly dangerous in environments where physical access or close-range wireless interference is possible. The vulnerability can be exploited to cause persistent denial of service conditions, rendering Bluetooth functionality unusable and potentially affecting device availability. The impact extends beyond simple service disruption as it can compromise the overall stability of IoT deployments that rely heavily on wireless connectivity for device management and communication. Organizations using ESP32-based devices for critical infrastructure or security applications face significant risk from this vulnerability.
Mitigation strategies for CVE-2021-28136 include immediate upgrading to ESP-IDF version 4.5 or later where the vulnerability has been addressed through proper packet validation and handling mechanisms. System administrators should implement network monitoring to detect unusual Bluetooth packet patterns that might indicate exploitation attempts. Device manufacturers should conduct thorough security testing of their Bluetooth implementations and consider implementing additional input validation layers. The vulnerability aligns with ATT&CK technique T1592, Pre-Attack, and T1499, Endpoint Denial of Service, as it enables attackers to disrupt device operations through wireless means. Organizations should also consider implementing Bluetooth radio access controls and monitoring for duplicate packet sequences to detect potential exploitation attempts. Patch management procedures should be enhanced to ensure timely updates of embedded firmware components, particularly in environments where physical security controls are limited.