CVE-2021-39789
📋 TL;DR
This vulnerability in Android's Telecom component allows local attackers to escalate privileges without user interaction by exploiting a missing permission check for TTY mode changes. It affects Android 12L devices, enabling attackers to gain elevated system access from a standard user context.
💻 Affected Systems
- Android
📦 What is this software?
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing installation of persistent malware, data theft, and full system control.
Likely Case
Local privilege escalation enabling unauthorized access to sensitive system functions and user data.
If Mitigated
Limited impact with proper Android security updates and app sandboxing in place.
🎯 Exploit Status
Requires local access but no user interaction; exploit likely requires understanding of Android Telecom internals.
🛠️ 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 available security updates. 3. Reboot device after installation.
🔧 Temporary Workarounds
Disable TTY mode
androidTurn off TTY functionality if not needed
Settings > Accessibility > TTY mode > TTY off
🧯 If You Can't Patch
- Restrict physical access to devices and implement strong device management policies
- Use Android Enterprise or MDM solutions to enforce security configurations and monitor for suspicious 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 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 updated beyond Android 12L or security patch level is March 2022 or later.📡 Detection & Monitoring
Log Indicators:
- Unusual TTY mode changes in system logs
- Privilege escalation attempts in security logs
Network Indicators:
- None - local exploit only
SIEM Query:
source="android_system" AND (event="TTY_mode_change" OR process="com.android.server.telecom")