CVE-2023-21130 - Android Bluetooth Vulnerability Explained – Remote Code Execution Exploit Walkthrough

In June 2023, security researchers discovered and reported CVE-2023-21130, a serious vulnerability in the Android Bluetooth subsystem. This issue stems from a buffer overflow in the way the system handles periodic Bluetooth LE advertisements. The consequences? An attacker can execute code remotely on a device without any user interaction or need for extra privileges.

Android Bluetooth vulnerabilities are rare but dangerous. Let's break down what CVE-2023-21130 is, how it works, and how attackers might exploit it, using practical explanations, code snippets, and simple examples. This post is exclusive: you won't find these insights elsewhere.

Impact: Remote Code Execution (RCE), no user interaction, no privileges required.

- Google Android ID: A-273502002

Original Reference

- Google Android Security Bulletin - June 2023

Technical Overview

At its core, the vulnerability lies in the handling of Bluetooth Low Energy (BLE) periodic advertising events. The function btm_ble_periodic_adv_sync_lost in the file btm_ble_gap.cc is responsible for cleaning up resources when the system loses synchronization with a periodic advertiser. Here, sloppy bounds checking causes a heap buffer overflow.

The BLE stack receives data from nearby devices wirelessly. If an attacker sends specially crafted periodic advertising packets, the processing function might write outside the bounds of a heap buffer, corrupting memory and enabling the attacker to execute their own code.

Here’s a simplified, illustrative version of the vulnerable function

// btm_ble_gap.cc

void btm_ble_periodic_adv_sync_lost(uint8_t sync_handle) {
    tBTM_BLE_SYNC* p_sync = btm_find_ble_sync_by_handle(sync_handle);
    if (p_sync) {
        // ... clean up logic ...
        memset(p_sync->data, , p_sync->data_length);  // 🔥 Vulnerable!
        // ... more logic ...
    }
}

What's wrong here?

- If p_sync->data_length is controlled by attacker input, and it is greater than the actual buffer size, memset() will overwrite neighboring memory.

Identify a target device running Android 13 (or earlier) with Bluetooth enabled.

2. Transmit crafted periodic advertising packets designed to desynchronize the BLE periodic advertising sync.
3. Manipulate sync parameters so the target's btm_ble_periodic_adv_sync_lost function is called with attacker-chosen values.

Inject and execute shellcode (for demonstration: cause a device crash or open a backdoor).

No user interaction is needed—the victim just needs Bluetooth enabled.

Proof-of-Concept (PoC) Outline

Below is a conceptual Python snippet using bleak (note: doesn't exploit the bug directly, but illustrates the attack vector).

import asyncio
from bleak import BleakScanner, BleakAdvertiser

async def fake_periodic_advertisement():
    # Not actual code - for illustration only
    # In reality, attacker would use custom hardware or firmware for full control 
    advertiser = BleakAdvertiser()
    custom_data = bytes([xAA]*128)  # Overflow data, length > expected
    while True:
        await advertiser.send_periodic(custom_data)  # Send repeatedly
        await asyncio.sleep(.1)

asyncio.run(fake_periodic_advertisement())

For a real exploit, the attacker would use a *low-level radio* to carefully craft BLE packets that trick the target device into running through the vulnerable code path.

Mitigation

Google fixed the issue in June 2023. All users and vendors are strongly advised to update their devices to the latest Android security patch level.

Temporary workaround: Disable Bluetooth when not in use.

Reference: Android Security Bulletin - June 2023

Conclusion

CVE-2023-21130 showcases how even small mistakes—like missing length checks—can enable serious remote attacks. Since Bluetooth is always on for many users, attackers can compromise devices quietly, without any clicks or interaction.

Device vendors should act fast to patch such issues.

For more details and ongoing research, watch the official Android Security Bulletins. Stay safe!

Timeline

Published on: 06/15/2023 19:15:00 UTC
Last modified on: 06/22/2023 13:39:00 UTC