CVE-2023-21108: Google Android Bluetooth RCE Vulnerability

CVE-2023-21108 Overview

CVE-2023-21108 is a critical Use After Free vulnerability in the Android Bluetooth stack, specifically in the sdpu_build_uuid_seq function of sdp_discovery.cc. This vulnerability allows an attacker within Bluetooth range to achieve remote code execution without requiring user interaction or additional execution privileges. The flaw occurs in the Service Discovery Protocol (SDP) implementation, which is fundamental to Bluetooth device communication.

Critical Impact

Remote code execution over Bluetooth with no user interaction required when Hands-Free Profile (HFP) support is enabled.

Affected Products

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

Discovery Timeline

• 2023-06-15 - CVE-2023-21108 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-21108

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption flaw that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of the Android Bluetooth stack, the vulnerable function sdpu_build_uuid_seq improperly handles memory during SDP discovery operations, leading to an out-of-bounds write condition.

The attack can be executed from an adjacent network position (Bluetooth range) with low complexity and no authentication requirements. When exploited, an attacker gains the ability to execute arbitrary code with the privileges of the Bluetooth service, potentially compromising confidentiality, integrity, and availability of the affected device.

Root Cause

The root cause lies in improper memory management within the SDP discovery implementation in Android's Bluetooth subsystem. The sdpu_build_uuid_seq function fails to properly validate memory state before accessing previously allocated buffers. When building UUID sequences during service discovery, the function may reference memory that has already been deallocated, creating a use-after-free condition that can be exploited for arbitrary code execution.

Attack Vector

The attack vector is adjacent network-based, requiring the attacker to be within Bluetooth range of the target device. The exploitation scenario involves:

1. The attacker establishes a Bluetooth connection with a vulnerable Android device
2. During the SDP discovery phase, specially crafted packets trigger the use-after-free condition in sdpu_build_uuid_seq
3. The attacker manipulates the freed memory to achieve controlled write operations
4. By carefully crafting the memory layout, the attacker can redirect execution flow to arbitrary code

The vulnerability is particularly dangerous because it requires no user interaction and can be exploited when Hands-Free Profile (HFP) support is enabled, which is common on most Android devices for hands-free calling functionality.

Detection Methods for CVE-2023-21108

Indicators of Compromise

• Unusual Bluetooth connection attempts from unknown or suspicious devices
• Unexpected crashes or restarts of the Bluetooth service (com.android.bluetooth)
• Anomalous SDP discovery traffic patterns with malformed UUID sequences
• Memory corruption indicators in Bluetooth process logs

Detection Strategies

• Monitor Android system logs for Bluetooth-related crashes with stack traces pointing to sdp_discovery.cc or sdpu_build_uuid_seq
• Implement network-level monitoring for unusual Bluetooth pairing requests or SDP queries
• Deploy mobile threat detection solutions capable of identifying exploitation attempts against Bluetooth stack vulnerabilities
• Review device logs for unexpected privilege escalation events following Bluetooth activity

Monitoring Recommendations

• Enable verbose logging for Bluetooth services during investigation periods
• Implement endpoint detection and response (EDR) solutions with mobile device support
• Monitor for unusual process behavior spawned by Bluetooth-related services
• Track firmware and security patch levels across the Android device fleet

How to Mitigate CVE-2023-21108

Immediate Actions Required

• Apply the June 2023 Android Security Bulletin patches immediately on all affected devices
• Disable Bluetooth on devices that cannot be immediately patched when not in active use
• Disable Hands-Free Profile (HFP) if not required for business operations
• Implement mobile device management (MDM) policies to enforce security updates

Patch Information

Google addressed this vulnerability in the Android Security Bulletin June 2023. The vulnerability is tracked internally by Google as Android ID: A-239414876. Organizations should ensure all Android devices running versions 11, 12, 12L, and 13 are updated with security patches dated June 2023 or later.

Workarounds

• Disable Bluetooth completely when not required for device functionality
• Set Bluetooth to non-discoverable mode to reduce attack surface
• Avoid pairing with unknown or untrusted Bluetooth devices
• Implement network segmentation to limit Bluetooth-accessible areas in enterprise environments
• Use SentinelOne Mobile Threat Defense to detect and block exploitation attempts