CVE-2020-12352: Linux Kernel Information Disclosure Flaw

CVE-2020-12352 Overview

CVE-2020-12352 is an improper access control vulnerability in BlueZ, the official Linux Bluetooth protocol stack. The flaw, part of the BleedingTooth family of Bluetooth vulnerabilities, allows an unauthenticated attacker within Bluetooth range to retrieve sensitive kernel stack memory contents from an affected Linux system. The issue is tracked under [CWE-909: Missing Initialization of Resource] and affects both the Linux kernel and the BlueZ user-space components. Exploitation requires adjacent network access over Bluetooth but no user interaction or prior authentication, making it relevant for any Linux device with Bluetooth enabled.

Critical Impact
An unauthenticated attacker within Bluetooth range can read uninitialized kernel stack memory, potentially exposing sensitive information that aids further exploitation of the affected host.

Affected Products

Linux Kernel (multiple versions through 5.9)
BlueZ Bluetooth protocol stack
Linux distributions shipping affected BlueZ packages (Ubuntu, Debian, Red Hat, SUSE, and derivatives)

Discovery Timeline

2020-11-23 - CVE-2020-12352 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-12352

Vulnerability Analysis

The vulnerability resides in the L2CAP (Logical Link Control and Adaptation Protocol) implementation within the Linux kernel Bluetooth subsystem. Specific A2MP (AMP Manager Protocol) handling paths process incoming Bluetooth frames using kernel stack buffers that are not fully initialized before being referenced. When the stack constructs responses or interprets attacker-controlled length fields, residual stack contents can be exposed to a remote peer.

The issue is classified as [CWE-909: Missing Initialization of Resource]. Because the affected code path is reachable from any paired or unpaired Bluetooth device within radio range, an attacker positioned nearby can repeatedly trigger the leak to harvest pointers, stack canaries, and other secrets useful for bypassing Kernel Address Space Layout Randomization (KASLR).

This flaw is commonly chained with the companion BleedingTooth issues, notably CVE-2020-12351, to convert an information disclosure into reliable remote code execution at kernel privilege level.

Root Cause

The kernel's A2MP and L2CAP packet handlers allocate stack structures and copy attacker-supplied length-prefixed data without ensuring that unused bytes are zeroed. When the kernel echoes structure contents back to the Bluetooth peer, uninitialized stack memory is transmitted. The combination of trusting attacker-controlled lengths and skipping initialization produces a readable leak primitive over the air.

Attack Vector

Exploitation requires Bluetooth proximity, typically within 10 meters for Class 2 radios but extendable using high-gain antennas. The attacker sends crafted L2CAP or A2MP frames to a target host where the kernel Bluetooth stack is active and bluetoothd is running. No pairing, authentication, or user interaction is required because the vulnerable handlers process frames before authentication checks. The attacker observes the responses to recover kernel memory contents.

No verified public exploitation code is reproduced here. Technical details and proof-of-concept material are available through the Packet Storm Exploit Advisory and the Intel Security Advisory SA-00435.

Detection Methods for CVE-2020-12352

Indicators of Compromise

Unexpected bluetoothd crashes, kernel oops messages, or BUG: traces referencing l2cap_core.c or a2mp.c in dmesg and /var/log/syslog.
Bursts of inbound L2CAP or A2MP frames from unpaired Bluetooth devices, particularly on servers and workstations that do not normally accept Bluetooth connections.
New or unexpected Bluetooth pairings appearing in /var/lib/bluetooth/ on hosts that should not be advertising.

Detection Strategies

Monitor kernel logs for Bluetooth subsystem errors, segmentation faults in bluetoothd, or messages indicating malformed L2CAP frames.
Audit running kernel versions against vendor advisories and flag hosts running BlueZ versions prior to the patched releases.
Use endpoint telemetry to detect Bluetooth interfaces being enabled on systems where Bluetooth is not part of the approved baseline.

Monitoring Recommendations

Inventory all Linux endpoints, IoT devices, and servers that ship with Bluetooth hardware and track whether the bluetooth kernel module is loaded.
Alert on modprobe bluetooth, rfkill unblock bluetooth, and systemctl start bluetooth events on hosts where Bluetooth is not authorized.
Forward kernel logs and bluetoothd journal entries to a centralized logging or SIEM platform for retention and correlation across the fleet.

How to Mitigate CVE-2020-12352

Immediate Actions Required

Apply distribution kernel and BlueZ updates from Ubuntu, Debian, Red Hat, SUSE, or other vendors that address the BleedingTooth advisories (CVE-2020-12351, CVE-2020-12352, CVE-2020-24490).
Disable Bluetooth on any Linux host where it is not operationally required, particularly servers, virtualization hosts, and exposed kiosks.
Restrict physical and radio proximity to high-value Linux endpoints until patching is verified.

Patch Information

Fixes are provided through upstream Linux kernel updates and BlueZ package releases distributed by Linux vendors. Refer to the Kernel Live Patch Security Notice LSN-0074-1 and the Intel Security Advisory SA-00435 for kernel version guidance. Administrators using livepatch services can apply kernel fixes without rebooting.

Workarounds

Unload the Bluetooth kernel modules with rmmod bluetooth btusb and blacklist them in /etc/modprobe.d/ on systems where Bluetooth is not required.
Stop and disable bluetooth.service via systemctl disable --now bluetooth to prevent bluetoothd from binding to vulnerable handlers.
Where Bluetooth is required, limit discoverability and restrict device pairing to known MAC addresses using BlueZ configuration policies.

bash

# Configuration example: disable Bluetooth on Linux hosts that do not require it
sudo systemctl stop bluetooth.service
sudo systemctl disable bluetooth.service
echo 'blacklist bluetooth' | sudo tee /etc/modprobe.d/disable-bluetooth.conf
echo 'blacklist btusb'      | sudo tee -a /etc/modprobe.d/disable-bluetooth.conf
sudo rmmod btusb bluetooth 2>/dev/null || true