CVE-2021-39782
📋 TL;DR
This vulnerability allows local attackers to modify the PLMN SIM file without proper permission checks, potentially enabling privilege escalation on affected Android devices. It affects Android 12L devices and requires no user interaction for exploitation.
💻 Affected Systems
- Android
📦 What is this software?
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
An attacker gains full control of the device, accesses sensitive telephony data, and potentially compromises other applications through privilege escalation.
Likely Case
Local privilege escalation allowing unauthorized access to telephony functions and potentially other system resources.
If Mitigated
No impact if patched or if device is not running vulnerable Android 12L version.
🎯 Exploit Status
No user interaction required, but requires local access to the device. Exploitation details not publicly documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android Security Bulletin for Android 12L (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 after installation.
🔧 Temporary Workarounds
Disable telephony services (if not needed)
androidRemove or disable SIM card if device doesn't require telephony functionality
Settings > Network & internet > Mobile network > Disable mobile data
🧯 If You Can't Patch
- Restrict physical access to devices
- Implement mobile device management (MDM) with strict access controls
🔍 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 still 12L but security patch level is March 2022 or later in Settings > About phone > Android security update.📡 Detection & Monitoring
Log Indicators:
- Unusual telephony service access attempts
- Permission denial logs for PLMN file access
Network Indicators:
- None (local exploit only)
SIEM Query:
source="android_logs" AND (event="permission_denied" AND resource="PLMN" OR event="telephony_service_access")