CVE-2021-39806
📋 TL;DR
This CVE describes a double-free vulnerability in Android's label_backends_android.c that could allow local privilege escalation during servicemanager startup. Attackers could corrupt memory to gain elevated privileges without user interaction. Only Android 12L devices are affected.
💻 Affected Systems
- Android
📦 What is this software?
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
Local attacker gains full system privileges, potentially compromising the entire device and accessing sensitive data.
Likely Case
Local privilege escalation allowing unauthorized access to system resources and services.
If Mitigated
No impact if patched or if attacker cannot trigger the specific initialization failure condition.
🎯 Exploit Status
Requires local access and ability to trigger specific initialization failure condition during servicemanager startup.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android Security Bulletin June 2022 or later
Vendor Advisory: https://source.android.com/security/bulletin/pixel/2022-06-01
Restart Required: Yes
Instructions:
1. Check for Android system updates in Settings > System > System update. 2. Install the June 2022 or later security patch. 3. Reboot device after installation.
🔧 Temporary Workarounds
No effective workarounds
allThis is a core Android system vulnerability requiring patching at the OS level.
🧯 If You Can't Patch
- Restrict physical access to devices
- Implement strict device management policies and monitor for suspicious local activity
🔍 How to Verify
Check if Vulnerable:
Check Android version in Settings > About phone > Android version. If it shows Android 12L and security patch level is before June 2022, device is vulnerable.Check Version:
adb shell getprop ro.build.version.release && adb shell getprop ro.build.version.security_patchVerify Fix Applied:
Verify security patch level is June 2022 or later in Settings > About phone > Android version > Android security update.📡 Detection & Monitoring
Log Indicators:
- Unusual servicemanager crashes or restart patterns during device boot
- Suspicious local process privilege escalation attempts
Network Indicators:
- None - this is a local exploit
SIEM Query:
Search for servicemanager crash events or unexpected privilege changes in Android system logs