CVE-2020-12352: Linux Kernel Information Disclosure Flaw

CVE-2020-12352 Overview

CVE-2020-12352 is a medium severity information disclosure vulnerability affecting the BlueZ Bluetooth stack in the Linux kernel. The vulnerability arises from improper access control in BlueZ, which may allow an unauthenticated attacker within Bluetooth radio range to potentially enable information disclosure via adjacent network access. This vulnerability is part of a collection of Bluetooth vulnerabilities collectively known as "BleedingTooth."

Critical Impact

An unauthenticated attacker within Bluetooth range can leak sensitive kernel stack information without user interaction, potentially aiding in bypassing kernel address space layout randomization (KASLR) and enabling further exploitation.

Affected Products

• Linux Kernel (multiple versions)
• BlueZ Bluetooth stack
• Systems with Bluetooth 4.0+ hardware enabled

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

This vulnerability is classified under CWE-909 (Missing Initialization of Resource), indicating that certain data structures in the BlueZ Bluetooth stack are not properly initialized before use. When processing certain Bluetooth A2MP (Alternate MAC/PHY Manager Protocol) packets, the kernel fails to initialize stack memory, leading to the potential disclosure of kernel stack contents to a remote attacker.

The attack requires adjacent network access (Bluetooth radio range), but does not require any privileges or user interaction. The impact is limited to confidentiality, with high potential for information leakage but no direct impact on integrity or availability of the affected system.

Root Cause

The root cause of CVE-2020-12352 is missing initialization of stack memory in the A2MP protocol implementation within BlueZ. When specific A2MP protocol packets are processed, kernel stack data that should have been zeroed out is instead returned to the attacker. This uninitialized memory can contain sensitive kernel pointers and other data that aid attackers in defeating security mitigations such as KASLR.

Attack Vector

The attack vector is adjacent network access via Bluetooth. An attacker must be within Bluetooth radio range (typically up to 100 meters for Class 1 devices) of the target system. The attacker sends specially crafted A2MP protocol packets to the target device's Bluetooth interface. The vulnerable code path processes these packets and returns responses containing uninitialized kernel stack memory.

The attack does not require authentication, user interaction, or any special privileges. The attacker simply needs:

1. A Bluetooth-capable device configured for packet injection
2. Proximity to the target device
3. Knowledge of the target's Bluetooth MAC address (which can be obtained through scanning)

Detection Methods for CVE-2020-12352

Indicators of Compromise

• Unexpected A2MP protocol activity in Bluetooth logs
• Unusual Bluetooth scanning behavior from nearby devices
• Multiple A2MP_GETINFO_REQ or A2MP_GETAMPASSOC_REQ packets from untrusted sources
• Evidence of Bluetooth device enumeration preceding the attack

Detection Strategies

• Monitor kernel logs for anomalous Bluetooth A2MP protocol activity
• Implement Bluetooth traffic analysis for unusual packet patterns
• Deploy endpoint detection and response (EDR) solutions that monitor kernel-level Bluetooth stack activity
• Use SentinelOne Singularity Platform to detect suspicious Bluetooth-related kernel behavior

Monitoring Recommendations

• Enable verbose Bluetooth logging on critical systems to capture protocol-level events
• Monitor for devices in discoverable mode that should not be exposed
• Implement network segmentation and Bluetooth access policies
• Review kernel audit logs for Bluetooth subsystem anomalies

How to Mitigate CVE-2020-12352

Immediate Actions Required

• Update the Linux kernel to patched versions immediately
• Disable Bluetooth on systems where it is not required
• Set Bluetooth controllers to non-discoverable mode when not actively pairing
• Apply kernel live patches where available (see Kernel Live Patch Security Notice LSN-0074-1)

Patch Information

Security patches addressing CVE-2020-12352 have been released for affected Linux kernel versions. For detailed patch information and updates, refer to the Intel Security Advisory SA-00435. Organizations should prioritize patching systems that have Bluetooth enabled and are deployed in environments where attackers could achieve physical proximity.

Workarounds

• Disable the Bluetooth subsystem entirely using kernel boot parameters (bluetooth.disable_hs=1 or blacklisting modules)
• Physically remove or disable Bluetooth hardware where feasible
• Implement strict physical security controls to limit attacker proximity
• Use Bluetooth USB adapters that can be physically disconnected when not needed

# Configuration example - Disable Bluetooth High Speed to mitigate BleedingTooth vulnerabilities
# Add to /etc/default/grub GRUB_CMDLINE_LINUX_DEFAULT:
bluetooth.disable_hs=1

# Alternatively, blacklist the Bluetooth kernel module:
echo "blacklist bluetooth" >> /etc/modprobe.d/bluetooth-blacklist.conf
echo "blacklist btusb" >> /etc/modprobe.d/bluetooth-blacklist.conf

# Update GRUB and reboot
update-grub
reboot