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CVE-2021-38788

7.5 HIGH

📋 TL;DR

A privilege escalation vulnerability in Allwinner R818 SoC Android Q SDK allows malicious apps to manipulate the background service. By setting the allowed background applications to zero and whitelisting themselves, attackers can force other apps to stop when entering background, causing denial of service. This affects devices using Allwinner R818 SoC with Android Q SDK V1.0.

💻 Affected Systems

Products:
  • Allwinner R818 SoC devices
Versions: Android Q SDK V1.0
Operating Systems: Android Q (Android 10)
Default Config Vulnerable: ⚠️ Yes
Notes: Only affects devices using the specific Allwinner R818 SoC with the vulnerable background service implementation in Android Q SDK V1.0.

📦 What is this software?

Android Q Sdk by Allwinnertech

View all CVEs affecting Android Q Sdk →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete denial of service for all non-whitelisted applications, rendering device functionality severely impaired as legitimate apps cannot run in background.

🟠

Likely Case

Targeted denial of service against specific applications, disrupting user experience and potentially affecting critical functionality.

🟢

If Mitigated

Limited impact if proper app sandboxing and permission controls prevent malicious apps from accessing the vulnerable service interface.

🌐 Internet-Facing: LOW - Exploitation requires local app installation, not directly internet exploitable.
🏢 Internal Only: MEDIUM - Requires malicious app installation, but could be delivered through sideloading or compromised app stores.

🎯 Exploit Status

Public PoC: ⚠️ Yes
Weaponized: LIKELY
Unauthenticated Exploit: ✅ No
Complexity: LOW

Exploitation requires app installation with permissions to access the background service interface. Public proof-of-concept details available in GitHub repository.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Unknown specific version - check with device manufacturer

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 latest firmware/OS updates. 3. Verify background service permissions are properly restricted in updated version.

🔧 Temporary Workarounds

Restrict app installation sources

android

Prevent installation of untrusted apps that could exploit this vulnerability

adb shell settings put secure install_non_market_apps 0

Monitor background service permissions

android

Regularly audit which apps have background service access permissions

adb shell dumpsys activity permissions | grep -i background

🧯 If You Can't Patch

  • Implement strict app vetting process to prevent malicious app installation
  • Use mobile device management (MDM) solutions to control app permissions and monitor for suspicious behavior

🔍 How to Verify

Check if Vulnerable:

Check device specifications for Allwinner R818 SoC and Android Q SDK V1.0. Review background service permission settings.

Check Version:

adb shell getprop ro.build.version.sdk && adb shell getprop ro.hardware

Verify Fix Applied:

Verify firmware version is updated beyond vulnerable SDK version. Test background app functionality remains intact.

📡 Detection & Monitoring

Log Indicators:

  • Unexpected background service permission changes
  • Multiple apps being force-stopped when entering background
  • Suspicious app requesting background service interfaces

Network Indicators:

  • None - local exploitation only

SIEM Query:

android_logs:background_service AND (permission_change OR force_stop)

📊 Metadata

CVE ID: CVE-2021-38788
CVSS v3 Score: 7.5 (HIGH)
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: January 19, 2022
Last Updated: November 21, 2024

🔗 References

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