CVE-2021-39726
📋 TL;DR
This CVE describes an out-of-bounds read vulnerability in the Android kernel's cd_ParseMsg function. It allows remote attackers to read memory beyond intended boundaries without user interaction, potentially exposing sensitive information. All Android devices running vulnerable kernel versions are affected.
💻 Affected Systems
- Android
📦 What is this software?
Android by Google
⚠️ Risk & Real-World Impact
Worst Case
Remote attacker gains unauthorized access to kernel memory, potentially exposing sensitive system information, cryptographic keys, or other protected data that could facilitate further attacks.
Likely Case
Information disclosure where attackers can read portions of kernel memory, potentially exposing system state information or other data that could aid in developing more sophisticated attacks.
If Mitigated
Limited impact with proper network segmentation and device hardening, though information disclosure still occurs if exploited.
🎯 Exploit Status
No authentication required but requires specific conditions to trigger the out-of-bounds read; no public exploit code known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: March 2022 Android security patch level 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 after installation.
🔧 Temporary Workarounds
Network segmentation
allRestrict network access to Android devices to minimize attack surface
Disable unnecessary services
androidTurn off Bluetooth, Wi-Fi, and other network services when not needed
🧯 If You Can't Patch
- Segment Android devices on isolated network segments
- Implement strict network access controls and monitor for unusual outbound connections
🔍 How to Verify
Check if Vulnerable:
Check Android security patch level in Settings > About phone > Android version > Security patch level. If before March 2022, device is vulnerable.Check Version:
adb shell getprop ro.build.version.security_patchVerify Fix Applied:
Verify security patch level shows March 2022 or later date after applying update.📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- Unexpected process crashes related to cd_codec
- Memory access violation logs
Network Indicators:
- Unusual network traffic to/from Android devices on unexpected ports
- Multiple connection attempts to Android services
SIEM Query:
source="android_kernel" AND (event_type="panic" OR event_type="oops") AND process="cd_codec"