CVE-2021-39629
📋 TL;DR
This CVE describes a use-after-free vulnerability in Android's NFC stack due to a race condition between initialization and cleanup functions. It allows local attackers to escalate privileges without user interaction, potentially gaining root access. Affected devices run Android versions 9 through 12.
💻 Affected Systems
- Android devices with NFC hardware
📦 What is this software?
Android by Google
Android by Google
Android by Google
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise with root privileges, allowing installation of persistent malware, data theft, and bypassing all security controls.
Likely Case
Local privilege escalation to system-level access, enabling installation of malicious apps, data access, and persistence mechanisms.
If Mitigated
Limited impact if SELinux policies are properly enforced and device is not rooted, though kernel-level access may still be possible.
🎯 Exploit Status
Exploitation requires local access and knowledge of race condition timing. No public exploits have been documented, but the vulnerability is well-documented in Android security bulletins.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android Security Patch Level 2022-01-01 and later
Vendor Advisory: https://source.android.com/security/bulletin/2022-01-01
Restart Required: Yes
Instructions:
1. Check for system updates in Settings > System > System update. 2. Install the January 2022 or later Android security patch. 3. Reboot the device after installation. 4. Verify the patch level in Settings > About phone > Android version.
🔧 Temporary Workarounds
Disable NFC functionality
androidTemporarily disable NFC to prevent exploitation of the vulnerable component
adb shell settings put secure nfc_on 0
Settings > Connected devices > Connection preferences > NFC (toggle off)
🧯 If You Can't Patch
- Disable NFC functionality completely through device settings
- Restrict physical access to devices and monitor for suspicious privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check Android security patch level: Settings > About phone > Android version > Android security patch level. If earlier than 2022-01-01, device is vulnerable.Check Version:
adb shell getprop ro.build.version.security_patchVerify Fix Applied:
Verify security patch level is 2022-01-01 or later. Check that NFC functionality works normally after patch.📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs related to NFC driver
- SELinux denials for NFC-related processes
- Unexpected privilege escalation in system logs
Network Indicators:
- None - this is a local exploit
SIEM Query:
source="android_logs" AND (process="nfc" OR process="phTmlNfc") AND (event="segfault" OR event="use-after-free" OR event="privilege_escalation")