CVE-2021-39809
📋 TL;DR
This vulnerability allows remote attackers to read memory beyond intended boundaries in Android's Bluetooth AVRCP (Audio/Video Remote Control Profile) component. Attackers could potentially leak sensitive information from affected devices without user interaction. All Android devices running versions 10 through 12L are affected.
💻 Affected Systems
- Android
📦 What is this software?
Android by Google
Android by Google
Android by Google
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
Remote information disclosure allowing attackers to read sensitive data from device memory, potentially including authentication tokens, encryption keys, or other protected information.
Likely Case
Limited information leakage from Bluetooth stack memory, potentially exposing device identifiers or Bluetooth-related data.
If Mitigated
No impact if patched; minimal risk if Bluetooth is disabled or device is not discoverable.
🎯 Exploit Status
Exploitation requires Bluetooth proximity and knowledge of the vulnerability. No authentication needed, but attacker must be within Bluetooth range.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android Security Bulletin April 2022 or later
Vendor Advisory: https://source.android.com/security/bulletin/2022-04-01
Restart Required: Yes
Instructions:
1. Check for system updates in Settings > System > System update. 2. Install the April 2022 Android security patch or later. 3. Reboot device after installation.
🔧 Temporary Workarounds
Disable Bluetooth
androidTurn off Bluetooth to prevent exploitation
Settings > Connected devices > Connection preferences > Bluetooth > Toggle off
Disable Bluetooth Discovery
androidMake device non-discoverable to reduce attack surface
Settings > Connected devices > Connection preferences > Bluetooth > Device name > Turn off 'Make device discoverable'
🧯 If You Can't Patch
- Disable Bluetooth when not in use
- Avoid using Bluetooth in public or untrusted environments
🔍 How to Verify
Check if Vulnerable:
Check Android version in Settings > About phone > Android version. If version is 10, 11, 12, or 12L and security patch level is before April 2022, device is vulnerable.Check Version:
Settings > About phone > Android versionVerify Fix Applied:
Verify security patch level is April 2022 or later in Settings > About phone > Android security patch level.📡 Detection & Monitoring
Log Indicators:
- Unusual Bluetooth connection attempts
- AVRCP protocol anomalies in Bluetooth logs
Network Indicators:
- Suspicious Bluetooth traffic patterns
- AVRCP vendor command anomalies
SIEM Query:
Not typically applicable for Bluetooth-based vulnerabilities on mobile devices