CVE-2021-47533
📋 TL;DR
This is a use-after-free vulnerability in the Linux kernel's VC4 display driver that could allow local attackers to cause kernel crashes or potentially execute arbitrary code. It affects systems using the VC4 driver for Broadcom VideoCore graphics, primarily Raspberry Pi devices and other embedded systems with this hardware. The vulnerability occurs when the kernel fails to clear a pointer after use, leading to potential memory corruption.
💻 Affected Systems
- Linux kernel with VC4 display driver
📦 What is this software?
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Local privilege escalation to kernel mode, allowing complete system compromise and arbitrary code execution at the highest privilege level.
Likely Case
Kernel panic or system crash leading to denial of service, with potential for limited information disclosure from kernel memory.
If Mitigated
System remains stable with no impact if patched or if the vulnerable driver is not in use.
🎯 Exploit Status
Exploitation requires local access and knowledge of kernel memory layout. No public exploits are known, but the vulnerability type (use-after-free) is commonly exploited.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel with commits 2931db9a5ed219546cf2ae0546698faf78281b89 or d134c5ff71c7f2320fc7997f2fbbdedf0c76889a
Vendor Advisory: https://git.kernel.org/stable/c/2931db9a5ed219546cf2ae0546698faf78281b89
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix. 2. For Raspberry Pi OS: 'sudo apt update && sudo apt upgrade'. 3. For other distributions: Use your package manager to update kernel packages. 4. Reboot the system to load the new kernel.
🔧 Temporary Workarounds
Disable VC4 driver
linuxPrevent loading of the vulnerable VC4 display driver module
echo 'blacklist vc4' | sudo tee /etc/modprobe.d/blacklist-vc4.conf
sudo update-initramfs -u
sudo reboot
🧯 If You Can't Patch
- Restrict local user access to systems using VC4 driver
- Implement strict privilege separation and limit users who can access display-related operations
🔍 How to Verify
Check if Vulnerable:
Check if VC4 driver is loaded: 'lsmod | grep vc4'. If loaded, check kernel version against patched versions.Check Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix: 'uname -r' and check if it's newer than vulnerable versions. Confirm VC4 driver loads without issues.📡 Detection & Monitoring
Log Indicators:
- Kernel oops messages
- System crashes/panics related to VC4 or display driver
- dmesg errors mentioning use-after-free or memory corruption
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
source="kernel" AND ("vc4" OR "use-after-free" OR "kernel panic")