CVE-2021-38786
📋 TL;DR
A NULL pointer dereference vulnerability in the media/libcedarc/vdecoder component of Allwinner R818 SoC Android Q SDK V1.0 allows attackers to cause a denial of service by crashing the media subsystem. This affects devices using the Allwinner R818 system-on-chip with the vulnerable Android Q SDK. The vulnerability requires local access or malicious media file processing to trigger.
💻 Affected Systems
- Allwinner R818 SoC-based devices
📦 What is this software?
Android Q Sdk by Allwinnertech
⚠️ Risk & Real-World Impact
Worst Case
Complete device crash or persistent denial of service requiring reboot, potentially disrupting critical media processing functions.
Likely Case
Media application crash when processing specially crafted media files, causing temporary service disruption.
If Mitigated
Limited impact with proper input validation and sandboxing, potentially only affecting the media decoder process.
🎯 Exploit Status
Requires ability to trigger media decoder with malicious input; likely requires local access or malicious app installation.
🛠️ 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 updated firmware 2. Apply manufacturer-provided patch 3. Reboot device after update
🔧 Temporary Workarounds
Restrict media file sources
allOnly allow media files from trusted sources and applications
Disable unnecessary media processing
androidLimit media decoder usage to essential applications only
🧯 If You Can't Patch
- Isolate affected devices from untrusted networks and media sources
- Implement application whitelisting to prevent untrusted apps from accessing media decoder
🔍 How to Verify
Check if Vulnerable:
Check device specifications for Allwinner R818 SoC and Android Q SDK version; review manufacturer security bulletins.Check Version:
Manufacturer-specific commands vary; typically check in Settings > About Phone > Build NumberVerify Fix Applied:
Verify with device manufacturer that latest firmware includes the security patch for CVE-2021-38786.📡 Detection & Monitoring
Log Indicators:
- Media decoder crash logs
- NULL pointer dereference errors in system logs
- Unexpected media service restarts
Network Indicators:
- Unusual media file transfers to affected devices
SIEM Query:
Search for 'vdecoder crash', 'NULL pointer', or 'media service restart' in device logs🔗 References
- https://github.com/pokerfacett/MY_CVE_CREDIT/blob/master/Allwinner%20R818%20SoC%EF%BC%9AMedia%20vdecoder%20has%20Null%20Pointer%20Dereference%20Vulnerability.md
- https://vul.wangan.com/a/CNVD-2021-49173
- https://www.allwinnertech.com/index.php?c=product&a=index&id=92
- https://www.cnvd.org.cn/flaw/show/CNVD-2021-49173
- https://github.com/pokerfacett/MY_CVE_CREDIT/blob/master/Allwinner%20R818%20SoC%EF%BC%9AMedia%20vdecoder%20has%20Null%20Pointer%20Dereference%20Vulnerability.md
- https://vul.wangan.com/a/CNVD-2021-49173
- https://www.allwinnertech.com/index.php?c=product&a=index&id=92
- https://www.cnvd.org.cn/flaw/show/CNVD-2021-49173
