CVE-2021-38789
📋 TL;DR
CVE-2021-38789 is an incorrect access control vulnerability in Allwinner R818 SoC Android Q SDK V1.0 where the aw_display service fails to verify caller permissions. This allows third-party Android apps to modify system settings without authorization. Devices using this specific SoC and SDK version are affected.
💻 Affected Systems
- Allwinner R818 SoC devices running Android Q
📦 What is this software?
Android Q Sdk by Allwinnertech
⚠️ Risk & Real-World Impact
Worst Case
Malicious app could change critical system settings like display resolution, brightness, or other hardware parameters, potentially causing system instability or denial of service.
Likely Case
Unauthorized apps could modify display settings, change system configurations, or interfere with device functionality without user consent.
If Mitigated
With proper permission checks, only system apps with appropriate privileges could modify system settings.
🎯 Exploit Status
Exploitation requires a malicious app to be installed on the device. The vulnerability is in the service permission checking mechanism.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android Q SDK V1.0 with security patches or later versions
Vendor Advisory: https://www.allwinnertech.com/index.php?c=product&a=index&id=92
Restart Required: Yes
Instructions:
1. Contact device manufacturer for firmware updates. 2. Apply Allwinner-provided patches for the aw_display service. 3. Update to patched Android Q SDK version. 4. Rebuild and flash device firmware.
🔧 Temporary Workarounds
Restrict app installation sources
androidOnly allow app installation from trusted sources like Google Play Store
Disable unknown sources
androidTurn off installation from unknown sources in Android settings
🧯 If You Can't Patch
- Implement app vetting process to prevent malicious apps from being installed
- Use mobile device management (MDM) solutions to control app installation and monitor for suspicious behavior
🔍 How to Verify
Check if Vulnerable:
Check device specifications for Allwinner R818 SoC and Android Q version. Review system logs for unauthorized aw_display service calls.Check Version:
adb shell getprop ro.build.version.sdk (should return 29 for Android Q) and check hardware specifications for SoCVerify Fix Applied:
Test with a controlled app attempting to call aw_display service without proper permissions - should be denied.📡 Detection & Monitoring
Log Indicators:
- Unauthorized calls to aw_display service
- Permission denial logs for system settings modification
Network Indicators:
- Not applicable - local vulnerability
SIEM Query:
source="android" AND (service="aw_display" OR permission_denied) AND action="modify_system_settings"🔗 References
- https://github.com/pokerfacett/MY_CVE_CREDIT/blob/master/Allwinner%20R818%20SoC%EF%BC%9Aaw_display%20service%20has%20EoP%20Vulnerability.md
- https://vul.wangan.com/a/CNVD-2021-46927
- https://www.allwinnertech.com/index.php?c=product&a=index&id=92
- https://www.cnvd.org.cn/flaw/show/CNVD-2021-46927
- https://github.com/pokerfacett/MY_CVE_CREDIT/blob/master/Allwinner%20R818%20SoC%EF%BC%9Aaw_display%20service%20has%20EoP%20Vulnerability.md
- https://vul.wangan.com/a/CNVD-2021-46927
- https://www.allwinnertech.com/index.php?c=product&a=index&id=92
- https://www.cnvd.org.cn/flaw/show/CNVD-2021-46927
