*Published: May 2024*


If you own or use an Android device—especially one running Android 11, 12, 12L, or 13—there’s a critical Bluetooth security bug you need to know about. Tracked as CVE-2023-21108, this vulnerability could let hackers run code on your phone *remotely*, without you even knowing. Let’s break down what happened, how it works, and why you should care.

What is CVE-2023-21108?

CVE-2023-21108 is a security issue in Android’s Bluetooth stack—specifically in handling Bluetooth’s Hands-Free Profile (HFP). In simple terms, the bug happens in the sdpu_build_uuid_seq function of the sdp_discovery.cc file. Due to a coding mistake, it's possible for an attacker to trigger a use-after-free bug, which can result in an out-of-bounds write. If you’re not a programmer, that basically means hackers can trick your phone into writing data where it shouldn’t—potentially taking over the device.

Android 13

Note: The device has to have Bluetooth Hands-Free Profile (HFP) enabled, which is common for phone-to-car or headset features.

The Function

Inside Android’s Bluetooth service, Service Discovery Protocol (SDP) helps devices find out what other Bluetooth devices can do. The crash-causing line is in this function:

void sdpu_build_uuid_seq(uint8_t* p, int max_len) {
    // ... code omitted
    free(p); // releases the pointer
    p[] = ... // accesses freed memory (use-after-free)
}

The program then writes data to p, but p doesn’t point to valid memory anymore.

3. This use-after-free can be exploited to overwrite important parts of memory—triggering code execution.

Realistic Exploit Scenario

An attacker with a malicious Bluetooth device can send specially crafted packets to your phone while Bluetooth is on. They exploit the bug in SDP handling to overflow into memory and execute their code, hijacking your phone.

Attack Demonstration (Sample Exploit Code)

Here’s a simplified *conceptual* Python snippet to demonstrate what an attacker might do (for educational purposes only):

# This is a *conceptual* attack illustration, not a real Bluetooth exploit!
import bluetooth

attacker_device = bluetooth.BluetoothSocket(bluetooth.RFCOMM)
attacker_device.connect(("victim_device_addr", 1))

# Malicious UUID sequence to trigger the bug
payload = b'\x35\xFF' + b'A' * 256  # Overlong sequence

attacker_device.send(payload)  # Triggers out-of-bounds write
attacker_device.close()

In reality, crafting the exact payload for RCE would need much more work and deep knowledge of Android internals.

Official References

- Google Android Issue Tracker (A-239414876)
- NVD CVE Entry
- Android Security Bulletin – March 2023

How Do I Stay Safe?

- Update Your Device: If you use Android 11, 12, 12L, or 13—update to the latest security patch ASAP.

Conclusion

CVE-2023-21108 is a dangerous Bluetooth bug in Android. With no action on your end, attackers could compromise your device just by being nearby. The good news? Google has patched this in recent updates. Make sure you’re running the latest Android security patch—and always treat software updates as *urgent*, not optional.

Stay secure!

*Feel free to share this post if you think someone you care about might be at risk.*

Timeline

Published on: 06/15/2023 19:15:00 UTC
Last modified on: 06/21/2023 12:54:00 UTC