---
In early 2024, security researchers discovered a critical vulnerability in the Linux kernel's Bluetooth subsystem, specifically impacting how device names are handled in the core Bluetooth code. This issue, tracked as CVE-2024-26889, could potentially result in a buffer overflow, risking system stability and even arbitrary code execution. The problem has been resolved, but understanding its causes and impact is essential for both kernel developers and system administrators.
In this post, we’ll break down what happened in plain language, walk through the vulnerable code, see how it was fixed, and explain why it matters to anyone using Linux systems.
What is CVE-2024-26889?
CVE-2024-26889 is a security hole in the Linux kernel's core Bluetooth code (hci_core), where a fixed-size buffer (name[8] in struct hci_dev_info) could be overwritten when longer Bluetooth device names are copied with unsafe functions.
How Did This Happen?
The problem was that the code used strcpy() to copy a device name (hdev->name) into the fixed-size array di.name. If the name was longer than 8 characters, this simple copy would write off the end of the di.name buffer, leading to a buffer overflow.
Vulnerable Code (Before the Patch)
// drivers/bluetooth/hci_core.c
struct hci_dev_info di;
...
strcpy(di.name, hdev->name);
di.name is only 8 bytes, but hdev->name could be longer, so any name longer than 7 bytes (plus a null terminator) would overwrite memory.
Why is This Dangerous?
Buffer overflows are dangerous because they overwrite adjacent memory. In the worst case, attackers could exploit this to execute arbitrary code with kernel privileges—one of the most severe types of exploits possible.
Even if it doesn’t get exploited that way, a buffer overflow often causes the kernel to crash. Either way, it’s something you *really* do not want in your Bluetooth stack.
How Was It Fixed?
The Linux kernel developers quickly patched the bug. Instead of the unsafe strcpy(), they switched to strscpy(). This newer function is safer because it lets you set the maximum number of bytes to copy, and always NUL-terminates as long as possible.
Secure Code (After the Patch)
// drivers/bluetooth/hci_core.c
struct hci_dev_info di;
...
strscpy(di.name, hdev->name, sizeof(di.name));
strscpy() won’t write more than sizeof(di.name) bytes, so even if hdev->name is longer, there’s no overflow.
Read the patch on the official LKML mail list here:
🔗 LKML Patch Reference
How Could It Have Been Exploited?
The most obvious attack vector would be a malicious Bluetooth device broadcasting a name longer than 8 bytes. When the Linux kernel receives such a name and tries to process it, the overflow occurs.
Here is a simple *proof of concept* (PoC) snippet for the kind of payload an attacker might use
# (Pseudo Python code – actual exploitation would be more complex and platform-specific)
from bluetooth import *
target_bdaddr = "XX:XX:XX:XX:XX:XX"
# Send a device name that's excessively long (e.g., 32 chars)
malicious_name = "A" * 32
# Create a fake Bluetooth device (using specialized tools)
# Advertise with malicious_name to nearby Linux hosts
Note: Crafting a real world kernel exploit is much trickier, but this shows the principle.
Any code or app that interacts with Bluetooth at the kernel level.
- Especially risky on devices scanning for or interacting with many unknown Bluetooth peers, such as laptops and IoT devices.
References
- CVE-2024-26889 Report at cve.org
- Linux Kernel Patch Discussion
- strscpy() Documentation
Wrap Up
CVE-2024-26889 shows how even minor oversights—like underestimating how long a Bluetooth device name might be—can have major security impacts. Thanks to the Linux kernel contributors, this one was patched quickly, with a simple but impactful change: always use safe string functions when working with fixed-size buffers in C.
Stay vigilant, keep your systems updated, and spread the word about simple secure coding practices!
*Written by a Linux security enthusiast, 2024. Exclusive analysis for this post.*
Timeline
Published on: 04/17/2024 11:15:10 UTC
Last modified on: 10/31/2024 16:35:10 UTC