CVE-2023-20951: Google Android RCE Vulnerability

CVE-2023-20951 Overview

CVE-2023-20951 is an out-of-bounds write vulnerability in the Android Bluetooth stack, specifically within the gatt_process_prep_write_rsp function of gatt_cl.cc. The vulnerability stems from a missing bounds check that allows attackers to write data beyond allocated memory boundaries. This flaw enables remote code execution without requiring any user interaction or additional execution privileges, making it particularly dangerous for affected Android devices.

Critical Impact

This vulnerability allows remote attackers to execute arbitrary code on vulnerable Android devices via Bluetooth GATT (Generic Attribute Profile) protocol without any user interaction required.

Affected Products

• Google Android 11.0
• Google Android 12.0
• Google Android 12.1 (Android 12L)
• Google Android 13.0

Discovery Timeline

• 2023-03-24 - CVE-2023-20951 published to NVD
• 2025-02-25 - Last updated in NVD database

Technical Details for CVE-2023-20951

Vulnerability Analysis

The vulnerability exists in the Bluetooth GATT client implementation within Android's Bluetooth stack. The gatt_process_prep_write_rsp function in gatt_cl.cc processes prepared write responses during GATT operations. The flaw is categorized as CWE-787 (Out-of-bounds Write), indicating that the code writes data past the end or before the beginning of the intended buffer.

The vulnerability is exploitable over a network attack vector with low attack complexity. No privileges are required on the target system, and the attack does not require any user interaction. A successful exploit compromises the confidentiality, integrity, and availability of the affected device completely.

Root Cause

The root cause of this vulnerability is a missing bounds check in the gatt_process_prep_write_rsp function. When processing GATT prepared write responses, the function fails to properly validate the length of incoming data before copying it into a fixed-size buffer. This oversight allows an attacker to send specially crafted Bluetooth packets that cause the function to write beyond the allocated buffer boundaries, corrupting adjacent memory regions.

Attack Vector

The attack can be executed remotely over Bluetooth by sending malicious GATT prepared write response packets to a vulnerable Android device. The attacker needs to be within Bluetooth range of the target device or leverage a network-based Bluetooth relay. The exploitation process involves:

1. Establishing a Bluetooth connection with the target device
2. Initiating a GATT operation that triggers prepared write handling
3. Sending a maliciously crafted prepared write response with oversized data
4. The missing bounds check allows memory corruption beyond the intended buffer
5. Careful manipulation of the overwritten memory enables arbitrary code execution

The vulnerability is particularly severe because it requires no user interaction and can be triggered without authentication, allowing attackers to silently compromise devices within Bluetooth range.

Detection Methods for CVE-2023-20951

Indicators of Compromise

• Unexpected Bluetooth connections or pairing requests from unknown devices
• Anomalous system crashes or reboots related to Bluetooth services
• Unusual Bluetooth stack behavior or service restarts logged in system logs
• Evidence of unauthorized code execution or privilege escalation following Bluetooth activity

Detection Strategies

• Monitor Android system logs for crashes in the Bluetooth process (com.android.bluetooth) with stack traces referencing gatt_cl.cc or GATT-related functions
• Implement Bluetooth traffic analysis to detect malformed GATT prepared write responses with abnormal payload sizes
• Deploy endpoint detection solutions that monitor for suspicious memory access patterns in the Bluetooth stack
• Review device security patch levels to identify unpatched Android systems vulnerable to CVE-2023-20951

Monitoring Recommendations

• Enable verbose Bluetooth logging on managed devices to capture detailed GATT transaction information
• Implement network-level monitoring for Bluetooth Low Energy (BLE) traffic anomalies where feasible
• Configure security information and event management (SIEM) systems to alert on Bluetooth-related crashes
• Regularly audit Android security patch levels across the device fleet to ensure timely updates

How to Mitigate CVE-2023-20951

Immediate Actions Required

• Apply the Android security patch from the March 2023 security bulletin immediately
• Disable Bluetooth on devices that cannot be patched when not actively in use
• Implement device management policies to enforce security patch level requirements
• Consider network segmentation to limit Bluetooth exposure in sensitive environments

Patch Information

Google addressed this vulnerability in the Android Security Bulletin March 2023. The patch adds proper bounds checking to the gatt_process_prep_write_rsp function, preventing the out-of-bounds write condition. Organizations should update affected Android devices to the 2023-03-01 security patch level or later.

The vulnerability is tracked internally by Google as Android ID A-258652631. Device manufacturers and carriers may release updates on varying schedules, so administrators should verify patch availability from their specific device vendors.

Workarounds

• Disable Bluetooth entirely on devices that cannot receive patches to eliminate the attack surface
• Keep Bluetooth in non-discoverable mode when not actively pairing with trusted devices
• Avoid Bluetooth pairing in public or untrusted locations where attackers may be present
• Implement mobile device management (MDM) policies to enforce Bluetooth restrictions on vulnerable devices

# Configuration example
# Disable Bluetooth via ADB for testing or emergency mitigation
adb shell settings put global bluetooth_on 0
adb shell svc bluetooth disable

# Check current Android security patch level
adb shell getprop ro.build.version.security_patch
# Output should be 2023-03-01 or later for this CVE to be patched