CVE-2021-39743
📋 TL;DR
This vulnerability in Android's PackageManager allows malicious apps to update the last usage time of other packages without proper permission checks. This could enable local privilege escalation attacks where an attacker gains 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
An attacker could gain full system-level privileges, potentially accessing sensitive data, installing persistent malware, or disabling security controls.
Likely Case
Malicious apps could escalate privileges to perform unauthorized actions like accessing protected system resources or other apps' data.
If Mitigated
With proper app sandboxing and security controls, impact would be limited to the compromised app's context.
🎯 Exploit Status
Requires malicious app installation. No user interaction needed for exploitation once app is installed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android 12L security updates from March 2022 or later
Vendor Advisory: https://source.android.com/security/bulletin/android-12l
Restart Required: Yes
Instructions:
1. Check for Android system updates in Settings > System > System update. 2. Install the latest security update. 3. Restart the device.
🔧 Temporary Workarounds
Restrict app installations
androidOnly allow installation of apps from trusted sources like Google Play Store
Settings > Security > Install unknown apps > Disable for all apps
🧯 If You Can't Patch
- Implement mobile device management (MDM) to control app installations
- Use Android Enterprise with work profiles to isolate corporate apps
🔍 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 March 2022, device is vulnerable.Check Version:
adb shell getprop ro.build.version.release && adb shell getprop ro.build.version.security_patchVerify Fix Applied:
Verify Android version is 12L with security patch level March 2022 or later in Settings > About phone > Android version.📡 Detection & Monitoring
Log Indicators:
- PackageManager logs showing unauthorized package usage time updates
- Security logs showing privilege escalation attempts
Network Indicators:
- None - this is a local exploit
SIEM Query:
source="android_logs" AND "PackageManager" AND "lastUsageTime" AND "unauthorized"