CVE-2021-0339
📋 TL;DR
This vulnerability in Android allows a malicious app to remain visible on screen while a legitimate app is brought to the foreground, potentially enabling local privilege escalation without extra permissions. It affects Android users on specific versions, requiring user interaction for exploitation.
💻 Affected Systems
- Android
📦 What is this software?
Android by Google
Android by Google
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
An attacker could overlay a malicious interface to trick users into interacting with it, leading to data theft, unauthorized actions, or further system compromise.
Likely Case
Malicious apps could display phishing screens or fake login prompts to steal credentials or sensitive information from users.
If Mitigated
With proper app vetting and user awareness, the risk is reduced to minor UI confusion or limited data exposure.
🎯 Exploit Status
Exploitation requires a malicious app to be installed and user interaction to trigger the overlay; no public proof-of-concept is widely known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security patch level 2021-02-01 or later
Vendor Advisory: https://source.android.com/security/bulletin/2021-02-01
Restart Required: Yes
Instructions:
1. Check for system updates in device settings. 2. Apply the Android security update dated 2021-02-01 or newer. 3. Restart the device after installation.
🔧 Temporary Workarounds
Disable unknown app installations
androidPrevent installation of apps from unknown sources to reduce the risk of malicious apps.
Navigate to Settings > Security > Install unknown apps and disable for all apps
Use app vetting tools
allEmploy mobile device management (MDM) or security software to scan and block suspicious apps.
🧯 If You Can't Patch
- Monitor for unusual app behavior or overlay prompts and educate users on phishing risks.
- Restrict device usage to trusted apps only and implement network segmentation to limit potential damage.
🔍 How to Verify
Check if Vulnerable:
Check the Android security patch level in Settings > About phone > Android version; if before 2021-02-01, the device is vulnerable.Check Version:
adb shell getprop ro.build.version.security_patchVerify Fix Applied:
Confirm the security patch level is 2021-02-01 or later in device settings after applying the update.📡 Detection & Monitoring
Log Indicators:
- Log entries showing unexpected app overlays or WindowContainer anomalies in system logs
Network Indicators:
- Unusual network traffic from apps displaying overlays, though this is less common
SIEM Query:
Search for events related to app foreground/background transitions or overlay permissions in Android device logs.