Realtek Vulnerability Allows Attackers to Trigger DoS Attack

A newly discovered vulnerability in Realtek’s Bluetooth Low Energy (BLE) SDK enables attackers to disrupt secure connections through protocol manipulation.

Designated as Premature Pairing Random Injection, this flaw affects the Realtek RTL8762EKF-EVB development platform running SDK v1.4.0.

Attackers exploit state machine violations in the BLE Secure Connections pairing process, causing persistent denial-of-service (DoS) conditions.

Technical Mechanism of the Exploit

The vulnerability stems from improper validation of Bluetooth protocol sequences during Secure Connections pairing.

According to the Bluetooth Core Specification v5.3 (Vol 3, Part H), the Pairing Random packet must only be processed after a successful Pairing Public Key exchange.

However, the affected SDK fails to enforce this sequence, allowing attackers to inject a malicious Pairing Random packet prematurely.

This protocol violation triggers undefined state transitions in the Security Manager Protocol (SMP) layer, causing pairing failures and connection termination.

The device enters an irrecoverable invalid state, blocking subsequent connection attempts.

Attackers require only proximity to the target device (within BLE range) and can execute the attack using modified tools like Android BLE stacks or Nordic Semiconductor sniffers with packet-injection capabilities.

Proof of Concept and Reproduction

The attack follows a reproducible sequence:

1. Initiation: The Attacker initiates BLE pairing with the target device.
2. Malicious Injection: The Attacker transmits a crafted Pairing Random packet before the Pairing Public Key exchange.
3. State Corruption: Target device accepts the invalid sequence, violating the SMP state machine.
4. DoS Activation: Pairing process aborts, rendering the device unresponsive to legitimate connection requests.

A Python PoC script (pairing_random_before_pairing_public_key.py) automates this attack by forcing premature packet injection. Testing confirms that repeated exploitation causes persistent service disruption.

Mitigation and Vendor Response

Realtek must implement strict state-validation logic in the SMP layer to resolve this flaw.

Critical fixes include:

• State Machine Enforcement: Reject Pairing Random packets received before Pairing Public Key exchange completion.
• Protocol Sequencing: Implement Bluetooth Core Specification-mandated message ordering checks.
• Debugging Aids: Add state-transition logging to identify out-of-sequence packets during development.

Until a patched SDK version is released, developers should monitor connection attempts for anomalous packet sequences and restrict BLE access to trusted devices.

This vulnerability underscores the critical importance of rigorous state-machine validation in Bluetooth security implementations.

Impact Summary:

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