Bluetooth is the heartbeat of wireless communication in our everyday devices – smartphones, headphones, smartwatches and more. But sometimes, even in this critical communication link, tiny oversights can open the doors to major security threats. Recently, such a vulnerability was found and tracked as CVE-2024-0039. In this long-read, we'll break down what went wrong, how attackers might exploit it, and what you can do to stay safe.

[Summary](#summary)

1. What is CVE-2024-0039?

CVE-2024-0039 is a security vulnerability in some Bluetooth protocol stacks – specifically, in the code that handles the Attribute Protocol (ATT). If exploited, this bug allows a remote attacker (within Bluetooth range) to execute code on your device without your interaction or extra privileges. In plain English: just having Bluetooth enabled may be enough for an attacker to take over your device.


2. Where’s The Problem? The Role of ATT and att_protocol.cc

Bluetooth’s Attribute Protocol (ATT) handles device data exchange. For example, your fitness band telling your phone how many steps you've done. The code in question lies in a source file called att_protocol.cc, which interprets and builds “value commands” from remote devices.


The Technical Heartbeat: Out-of-Bounds Write

Let’s get to the code. In the function attp_build_value_cmd, user-controlled input determines how much data to “write” into a buffer. Because there is no check to ensure this data actually fits, attackers can overflow the buffer, corrupt memory, and potentially inject and execute code.

Here’s how it *should* look, in simplified form

// Vulnerable (simplified)
uint8_t buffer[MTU_SIZE];
int data_len = ...; // comes from remote device
memcpy(buffer, input_data, data_len); // no bounds check!

If data_len is bigger than MTU_SIZE, the buffer overflows, and attacker data spills into parts of memory they should never touch.

A proper fix involves checking bounds

if (data_len <= MTU_SIZE) {
    memcpy(buffer, input_data, data_len);
} else {
    // Drop, ignore, or log the error
}

Bug: Missing bounds check on input length.

4. How Does Exploitation Work? (With Example Payload)

An attacker can craft a Bluetooth ATT packet that claims to have more data than the receiving device’s memory allocation expects. When the device processes the packet, it writes past the end of a buffer in memory.

Example Exploit Snippet (Python, using Scapy and Bluetooth stack)

# Do not run on non-test devices! For research/demo only.

from scapy.all import *
from scapy.layers.bluetooth import *

# Malicious ATT Write Request with oversized payload
pkt = BTLE() / BTLE_ADV() / ATT_Write_Request(handle=x0001, value=b"A" * 1024)
sendp(pkt, iface="hci")

The malformed value is much larger than expected. If the remote device is vulnerable, this will trigger the overflow and potentially execute the attacker’s code.

Why is this dangerous? Devices handle Bluetooth connections *automatically*, so the user doesn’t need to approve or even know what’s happening.


No special permissions: Attackers don’t need to pair with your device.

- All sorts of devices affected: Phones, smartwatches, laptops, and even IoT gadgets, if they use the affected stack/code.


6. Am I Vulnerable? Which Devices Are Affected?

- Android devices: Many Androids use versions of the BlueDroid or Fluoride Bluetooth stack, which may be vulnerable if not patched.
- Linux/Bluetoothd based systems: Some Linux desktops, laptops and IoT devices using BlueZ.

Check advisories from your device or OS vendor!

7. Official References

- NIST NVD – CVE-2024-0039 (may update as details are public)
- Android Security Bulletin (June 2024)
- Bluetooth SIG Security Notices
- Patch for att_protocol.cc in AOSP (if/when available)


9. Summary

CVE-2024-0039 is a powerful reminder that even common, “invisible” frameworks like Bluetooth can contain dangerous flaws. A missing bounds check in attp_build_value_cmd opens the door to serious, remote code execution attacks—all without needing your permission. Stay safe by keeping your devices current and being smart about your connectivity.


If you’re a developer: Audit your input paths. Always check lengths before copying data. If you’re a user, patch and stay alert for security updates.


##### *Exclusively written for awareness. Reposting with credit is appreciated. If you want technical help, join bluetooth-dev Google Group.*

Timeline

Published on: 03/11/2024 17:15:45 UTC
Last modified on: 11/26/2024 14:26:56 UTC