The Linux kernel is the beating heart of many systems, from servers to smartphones. Security vulnerabilities here can be especially dangerous. In late 2022, researchers discovered a critical infoleak bug that could let remote attackers peek into sensitive kernel memory—all thanks to a flaw in Bluetooth's L2CAP protocol code.

This exclusive post will break down the bug, explain how it can be exploited to leak kernel pointers remotely, and show you the patch that fixed it. We’re using plain English and practical examples, so even if you don’t live in the kernel, you’ll understand what’s going on.

What Is CVE-2022-42895?

CVE-2022-42895 is a security vulnerability in the Linux kernel code handling Bluetooth connections—specifically in the file net/bluetooth/l2cap_core.c.

The problem happens in a function called l2cap_parse_conf_req. Its job is to process configuration requests for Bluetooth’s L2CAP connections. Because of an error, the function could accidentally copy out kernel memory contents (like pointer addresses) in response to crafted data sent over Bluetooth.

Why does that matter? Kernel pointer leaks are a gold mine for attackers. Modern Linux setups use a security technique called KASLR (Kernel Address Space Layout Randomization) to make attacks harder, but leaking pointers can totally defeat that.

This bug was fixed by this Linux commit

- https://github.com/torvalds/linux/commit/b1a2cd50c0357f243b7435a732b4e62ba3157a2e

Let’s look at the important parts

> Vulnerable function (net/bluetooth/l2cap_core.c)

static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data_len, ...)
{
    struct l2cap_conf_efs *efs;    // <-- Extended Features Structure
    ...
    /* parsing logic - overly trusting incoming data length */
    ...
}


The function improperly trusts the configuration option lengths sent by remote Bluetooth devices. If you send a specially-crafted packet, you can make the function dump out uninitialized stack or heap memory—containing goodies like kernel addresses.

Example of failing to sanitize incoming data:

If the code does something like this

memcpy(local_buf, option_data, option_len);  // No strict length check!


and doesn’t make sure option_len is sane or restrict it to actual struct size, attackers can pull out whatever was sitting in memory.

To exploit this bug, here’s roughly what an attacker would do

1. Initiate a Bluetooth L2CAP connection with a vulnerable Linux device (for example, a phone running an old kernel, or a server with Bluetooth enabled).

2. Send a malicious Configuration Request (L2CAP_CONF_REQ) with extended option data and lengths set to unexpected high/invalid values.

3. The vulnerable kernel responds with a Configuration Response (L2CAP_CONF_RSP), echoing back certain data, now infested with kernel memory.

4. Sniff the response for leaks, harvesting kernel pointers (addresses), which can then be used to bypass security (like KASLR), or to further attack the kernel and escalate privileges.

> Note: Attackers do not need to be authenticated—the attack works over the air.

Exploit Details and Proof-of-Concept

Let’s walk through a basic proof-of-concept. You’d need Bluetooth hardware and a userland tool like bluez, l2ping, or even Python/Scapy.

Pseudo-code (Python-like)

import bluetooth

target_addr = 'FF:AA:BB:CC:DD:EE'  # Replace with vulnerable target device

# Prepare malicious configuration request (crafted for infoleak)
malicious_packet = craft_l2cap_conf_req(option_type=xXX, option_len=xFF, option_data='A' * 255)

sock = bluetooth.BluetoothSocket(bluetooth.L2CAP)
sock.connect((target_addr, x1001))

sock.send(malicious_packet)

# Capture and analyze the response to find kernel pointers
response = sock.recv(1024)
analyze_infoleak(response)

What comes out?
The response can contain raw kernel memory—including addresses of functions, objects, etc.

Original References & Further Reading

- Linux Kernel Patch Commit
- NVD: CVE-2022-42895
- HackerOne Report (similar Bluetooth bugs)

How To Fix

Upgrade your kernel to any version that includes (or is newer than) commit b1a2cd50c0357f243b7435a732b4e62ba3157a2e. All major distros have released patches since late 2022.

Disable Bluetooth if you don’t need it, especially on servers!

*Stay safe, keep those kernels patched, and watch out for blue smoke! 🚨🐧*

Do you have questions or want to explore other Bluetooth vulnerabilities? Drop your thoughts below!

Timeline

Published on: 11/23/2022 15:15:00 UTC
Last modified on: 01/23/2023 18:29:00 UTC