Bluetooth is everywhere—in your headphones, cars, laptops, and IoT gadgets. But a serious security bug was discovered in BlueZ, one of the most widely used Bluetooth stacks in Linux devices. Identified as CVE-2023-27349, this vulnerability could allow hackers nearby to run their own code as root. If you use Linux and Bluetooth, this post is for you.

BlueZ handles core Bluetooth protocols in Linux, including the Audio/Video Remote Control Profile (AVRCP), responsible for features like play/pause/track-skip on media devices. In early 2023, researchers at Zero Day Initiative (ZDI) found that BlueZ did not properly validate data in a specific AVRCP message. Let's break down how this misstep could let someone take over a targeted device.

What Is the Vulnerability, in Plain English?

CVE-2023-27349 is caused by BlueZ not properly checking certain data it receives over Bluetooth when handling AVRCP messages. More specifically:

BlueZ (up to at least v5.66) does not carefully check the array index for AVRCP messages.

- Malicious values in these messages can make BlueZ write data past the end of a buffer (buffer overflow).
- With this, an attacker can carefully craft a Bluetooth packet that triggers the bug and injects code, running with root privileges.

It means: If a victim connects to a hacker’s rigged Bluetooth device, the attacker can take over the victim’s Linux box.

Technical Details: What’s Under the Hood?

The flaw sits in BlueZ’s AVRCP parsing logic. AVRCP messages include index values and commands for things like track lists and metadata. BlueZ’s code did not check if the received index was within the allocated memory bounds before using it, so if a specially crafted message included a large number, it led BlueZ to write data outside the expected area.

Code Example (Vulnerable Pattern)

> Note: This is a simplified illustration—NOT the real BlueZ code, but it shows the type of risky logic:

void avrcp_handle_get_element_attributes(uint8_t *params, size_t len) {
    uint8_t attr_count = params[]; // Get number of attributes
    uint8_t attr_ids[attr_count];   // Allocate array based on user input
    
    // Fill attributes from input (no bound check!)
    for (int i = ; i < attr_count; i++) {
        attr_ids[i] = params[i + 1];
    }
    // ... work with attr_ids
}

If attr_count is much larger than params or the buffer allows, this will stomp all over memory—a classic buffer overflow.

Attacker must be nearby (Bluetooth range, usually a few meters).

- Target must actively connect to the attacker’s rogue Bluetooth device (such as when pairing headphones, speakers, or a car system).

Attack Chain

1. Setup: Attacker creates a malicious Bluetooth device (could be a laptop, Raspberry Pi, or any device running custom Bluetooth software).

Lure: Victim attempts to connect to this device, thinking it’s safe.

3. Payload: The rogue device sends AVRCP commands/messages with out-of-bounds values.
4. Trigger: BlueZ on the victim’s device processes the message, but the bad index value lets the hacker overwrite crucial parts of memory.

Result: Hacker injects and runs code as root, getting full control.

> User interaction is required—the victim has to initiate a Bluetooth connection to the attacker.

Zero Day Initiative (ZDI) ZDI-CAN-19908:

https://www.zerodayinitiative.com/advisories/ZDI-CAN-19908/

BlueZ project page:

http://www.bluez.org/

NVD Entry for CVE-2023-27349:

https://nvd.nist.gov/vuln/detail/CVE-2023-27349

Official Patch Discussion:

https://lore.kernel.org/linux-bluetooth/

How to Protect Yourself

- Update BlueZ: Install the latest security updates from your Linux distribution as soon as possible.
- Don’t connect to unknown Bluetooth devices. If you see a new device show up for pairing, think twice before connecting.

Final Thoughts

Bluetooth vulnerabilities are extra risky because they often don’t need an internet connection. CVE-2023-27349 is especially serious because it grants full root access to attackers in your physical space—but it also reminds us to be careful with what we connect to, even over something as familiar as Bluetooth.

Timeline

Published on: 05/03/2024 02:15:13 UTC
Last modified on: 06/10/2024 17:16:11 UTC