CVE-2021-38787
📋 TL;DR
An integer overflow vulnerability exists in the ION driver of Allwinner R818 SoC Android Q SDK V1.0. Attackers can exploit this via the COMPAT_ION_IOC_SUNXI_FLUSH_RANGE ioctl command to cause a kernel crash, resulting in denial of service. This affects devices using the Allwinner R818 SoC with the vulnerable Android Q SDK.
💻 Affected Systems
- Allwinner R818 SoC-based devices
📦 What is this software?
Android Q Sdk by Allwinnertech
⚠️ Risk & Real-World Impact
Worst Case
Complete system crash requiring physical reboot, potentially leading to permanent device instability if repeatedly exploited.
Likely Case
Temporary denial of service requiring device restart, disrupting device functionality.
If Mitigated
No impact if patched or if vulnerable ioctl is blocked.
🎯 Exploit Status
Exploit requires local access to device (via malicious app or local user). The GitHub reference contains technical details that could be used to create an exploit.
🛠️ 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 firmware update. 3. Reboot device. 4. Verify patch is applied by checking kernel version or testing vulnerability.
🔧 Temporary Workarounds
Restrict /dev/ion access
linuxChange permissions on /dev/ion to restrict access to trusted processes only
chmod 600 /dev/ion
chown root:root /dev/ion
SELinux/AppArmor policy
linuxImplement mandatory access control to block unauthorized access to ION driver
🧯 If You Can't Patch
- Implement strict app vetting process to prevent malicious apps from accessing device
- Monitor system logs for crash events related to ION driver or kernel panics
🔍 How to Verify
Check if Vulnerable:
Check if device uses Allwinner R818 SoC and Android Q SDK V1.0: 'cat /proc/cpuinfo' and 'getprop ro.build.version.sdk'Check Version:
getprop ro.build.version.sdk && cat /proc/versionVerify Fix Applied:
Test if COMPAT_ION_IOC_SUNXI_FLUSH_RANGE ioctl still causes crash, or check with manufacturer for patch confirmation📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- ION driver crash logs
- System reboot events without clear cause
Network Indicators:
- None - local exploit only
SIEM Query:
source="kernel" AND ("panic" OR "ION" OR "flush_range")🔗 References
- https://github.com/pokerfacett/MY_CVE_CREDIT/blob/master/Allwinner%20R818%20SoC%EF%BC%9AION%20Driver%20Integer%20Overflow.md
- https://vul.wangan.com/a/CNVD-2021-49171
- https://www.allwinnertech.com/index.php?c=product&a=index&id=92
- https://www.cnvd.org.cn/flaw/show/CNVD-2021-49171
- https://github.com/pokerfacett/MY_CVE_CREDIT/blob/master/Allwinner%20R818%20SoC%EF%BC%9AION%20Driver%20Integer%20Overflow.md
- https://vul.wangan.com/a/CNVD-2021-49171
- https://www.allwinnertech.com/index.php?c=product&a=index&id=92
- https://www.cnvd.org.cn/flaw/show/CNVD-2021-49171
