CVE-2021-0507: Google Android Bluetooth RCE Vulnerability

CVE-2021-0507 Overview

CVE-2021-0507 is an out-of-bounds write vulnerability in the Android Bluetooth stack, specifically in the handle_rc_metamsg_cmd function of btif_rc.cc. This memory corruption flaw stems from a missing bounds check that can be exploited to achieve remote code execution over Bluetooth without requiring any user interaction or additional execution privileges.

Critical Impact

This vulnerability enables remote code execution over Bluetooth on affected Android devices without user interaction, potentially allowing attackers within Bluetooth range to fully compromise the device.

Affected Products

• Google Android 8.1
• Google Android 9.0
• Google Android 10.0
• Google Android 11.0

Discovery Timeline

• 2021-06-21 - CVE-2021-0507 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-0507

Vulnerability Analysis

The vulnerability resides in the Android Bluetooth Interface (BTIF) subsystem, specifically within the AVRCP (Audio/Video Remote Control Profile) message handling code. The handle_rc_metamsg_cmd function in btif_rc.cc processes metadata commands received over Bluetooth connections but fails to properly validate the bounds of incoming data before writing it to memory buffers.

This out-of-bounds write condition (CWE-787) occurs when the function processes specially crafted AVRCP metadata messages. Without proper validation, an attacker can supply malformed data that exceeds expected buffer boundaries, leading to memory corruption in the Bluetooth service process.

The vulnerability is particularly dangerous because it requires no user interaction and operates at the system level within the Bluetooth stack. An attacker within adjacent network range (Bluetooth proximity) can send malicious packets to trigger the vulnerability.

Root Cause

The root cause is a missing bounds check in the handle_rc_metamsg_cmd function when processing AVRCP remote control metadata commands. The function accepts incoming Bluetooth message data without validating that the data length falls within the expected buffer size, allowing writes beyond allocated memory regions. This is a classic out-of-bounds write vulnerability stemming from insufficient input validation in the Bluetooth protocol handling code.

Attack Vector

The attack is conducted over Bluetooth from an adjacent network position, meaning the attacker must be within Bluetooth radio range of the target device (typically within 10-100 meters depending on Bluetooth class). The attack requires:

1. The attacker establishes or hijacks a Bluetooth connection with the target Android device
2. The attacker sends specially crafted AVRCP metadata messages designed to trigger the out-of-bounds write
3. The malformed data overwrites critical memory structures in the Bluetooth service
4. Successful exploitation leads to arbitrary code execution with the privileges of the Bluetooth service

No user interaction is required, and no special privileges are needed on the attacker's side. The victim's device simply needs to have Bluetooth enabled and be within range.

Detection Methods for CVE-2021-0507

Indicators of Compromise

• Unexpected crashes or restarts of the Bluetooth service (com.android.bluetooth)
• Anomalous Bluetooth connection attempts from unknown devices
• Unusual AVRCP metadata traffic patterns in Bluetooth logs
• Memory corruption signatures in system crash dumps related to btif_rc.cc

Detection Strategies

• Monitor Android system logs for Bluetooth service crashes with stack traces pointing to handle_rc_metamsg_cmd or btif_rc.cc
• Implement Bluetooth traffic analysis to detect malformed AVRCP messages with abnormal payload sizes
• Deploy endpoint detection solutions capable of monitoring Bluetooth stack integrity
• Utilize Mobile Device Management (MDM) solutions to track device security patch levels

Monitoring Recommendations

• Enable verbose Bluetooth logging on managed devices for forensic analysis capabilities
• Implement network-level Bluetooth monitoring in high-security environments
• Configure alerting for repeated Bluetooth service failures on enterprise devices
• Maintain an inventory of device patch levels to identify vulnerable Android versions

How to Mitigate CVE-2021-0507

Immediate Actions Required

• Apply the Android security update from the June 2021 Security Bulletin immediately
• Disable Bluetooth on devices that cannot be immediately patched if they are in high-risk environments
• Restrict Bluetooth pairing to known devices only using device management policies
• Consider implementing Bluetooth discovery mode restrictions on vulnerable devices

Patch Information

Google addressed this vulnerability in the Android Security Bulletin June 2021. The patch adds proper bounds checking to the handle_rc_metamsg_cmd function to prevent out-of-bounds memory writes. The vulnerability is tracked internally by Google as Android ID A-181860042.

Organizations should ensure all Android devices are updated to security patch level 2021-06-01 or later. For devices that can no longer receive security updates, consider device replacement or implementing compensating controls.

Workarounds

• Disable Bluetooth entirely on devices that cannot be patched
• Enable Bluetooth only when actively needed and disable it immediately after use
• Configure devices to be non-discoverable and reject pairing requests from unknown devices
• Implement physical security controls to prevent proximity-based Bluetooth attacks in sensitive areas
• Use MDM policies to enforce Bluetooth usage restrictions on managed devices

# Android ADB command to disable Bluetooth (requires root or system access)
adb shell settings put global bluetooth_on 0

# Check current Android security patch level
adb shell getprop ro.build.version.security_patch

# Expected output for patched devices: 2021-06-01 or later