CVE-2021-39784
📋 TL;DR
CVE-2021-39784 is a local privilege escalation vulnerability in Android's CellBroadcastReceiver component. It allows attackers to enable specific cellular features without proper permission checks, potentially leading to unauthorized access to sensitive system functions. This affects Android 12L devices.
💻 Affected Systems
- Android
📦 What is this software?
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
An attacker could gain elevated system privileges, potentially enabling unauthorized cellular network access, intercepting communications, or disabling security features.
Likely Case
Local attackers could bypass cellular feature restrictions, potentially enabling unauthorized emergency alerts or network configuration changes.
If Mitigated
With proper patching, the vulnerability is eliminated; without patching, Android's sandboxing and other security layers provide partial protection.
🎯 Exploit Status
Exploitation requires local access and knowledge of the specific cellular features to target. No public exploit code is known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android Security Bulletin 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 March 2022 or later security patch. 3. Restart the device after installation.
🔧 Temporary Workarounds
Disable CellBroadcastReceiver (if possible)
androidDisabling the vulnerable component may reduce attack surface, but this could impact emergency alert functionality.
adb shell pm disable-user --user 0 com.android.cellbroadcastreceiver
🧯 If You Can't Patch
- Restrict physical access to devices and monitor for suspicious app installations.
- Use mobile device management (MDM) solutions to enforce security policies and detect anomalous behavior.
🔍 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, it 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 March 2022 or later in Settings > About phone > Android version > Android security update.📡 Detection & Monitoring
Log Indicators:
- Unusual CellBroadcastReceiver activity logs
- Permission denial attempts for cellular features
Network Indicators:
- Unexpected cellular network configuration changes
SIEM Query:
source="android_logs" AND component="CellBroadcastReceiver" AND action="permission_denied"