CVE-2021-39793
📋 TL;DR
This CVE describes a local privilege escalation vulnerability in the Mali GPU kernel driver for Android. An attacker could exploit a logic error in memory pinning code to write out of bounds, gaining elevated privileges without user interaction. This affects Android devices with vulnerable kernel versions.
💻 Affected Systems
- Android devices using Mali GPU drivers
📦 What is this software?
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
Full device compromise allowing attacker to execute arbitrary code with kernel privileges, bypassing all Android security sandboxes and gaining persistent access.
Likely Case
Local privilege escalation allowing malicious apps to break out of Android's application sandbox, access sensitive data, or install persistent malware.
If Mitigated
Limited impact if SELinux policies restrict the vulnerable driver or if the device has additional hardware-based security protections.
🎯 Exploit Status
Requires local access but no user interaction. The vulnerability is in kernel space, making exploitation more complex but feasible for skilled attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Android security patch level March 2022 or later
Vendor Advisory: https://source.android.com/security/bulletin/pixel/2022-03-01
Restart Required: Yes
Instructions:
1. Check for Android system updates in Settings > System > System update. 2. Install March 2022 or later security patch. 3. Reboot device to apply kernel updates.
🔧 Temporary Workarounds
Disable Mali GPU driver (not recommended)
linuxTemporarily disable the vulnerable driver module, but this will break GPU acceleration and many apps.
rmmod mali_kbase
🧯 If You Can't Patch
- Restrict app installations to trusted sources only via Android Enterprise or MDM policies
- Implement network segmentation to isolate vulnerable devices from critical resources
🔍 How to Verify
Check if Vulnerable:
Check Android security patch level in Settings > About phone > Android version. If before March 2022, device is likely vulnerable.Check Version:
adb shell getprop ro.build.version.security_patchVerify Fix Applied:
Verify security patch level shows March 2022 or later. Check kernel version with 'uname -r' and ensure it's updated.📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- SELinux denials related to mali_kbase
- Unexpected privilege escalation attempts
Network Indicators:
- Unusual outbound connections from privileged processes
- C2 communication from system-level processes
SIEM Query:
process:privilege_escalation AND driver:mali_kbase OR process:anomalous_kernel_access