CVE-2021-47200
📋 TL;DR
This is a use-after-free vulnerability in the Linux kernel's Direct Rendering Manager (DRM) subsystem that allows local attackers to potentially escalate privileges or crash the system. The vulnerability occurs when mmap operations on graphics memory objects incorrectly handle reference counting, leading to memory corruption. Any system running an affected Linux kernel version with DRM/prime functionality enabled is vulnerable.
💻 Affected Systems
- Linux kernel
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Local privilege escalation to root, kernel panic leading to denial of service, or arbitrary code execution in kernel context.
Likely Case
Kernel crash/panic causing system instability or denial of service, potentially allowing privilege escalation in specific configurations.
If Mitigated
Limited impact due to SELinux/AppArmor restrictions, container isolation, or lack of local access.
🎯 Exploit Status
Exploitation requires local access and knowledge of kernel memory layout. The vulnerability is in a specific graphics subsystem path.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in kernel commits 4f8e469a2384dfa4047145b0093126462cbb6dc0 and 8244a3bc27b3efd057da154b8d7e414670d5044f
Vendor Advisory: https://git.kernel.org/stable/c/4f8e469a2384dfa4047145b0093126462cbb6dc0
Restart Required: Yes
Instructions:
1. Update to a kernel version containing the fix commits. 2. Check your distribution's security advisories for patched kernel packages. 3. Reboot the system after kernel update.
🔧 Temporary Workarounds
Disable DRM/prime functionality
linuxDisable the affected graphics subsystem if not needed
echo "blacklist drm" > /etc/modprobe.d/disable-drm.conf
update-initramfs -u
reboot
🧯 If You Can't Patch
- Restrict local user access and implement strict privilege separation
- Enable kernel security features like SELinux/AppArmor to limit impact
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if it contains the vulnerable commit: uname -r and examine kernel source or distribution security advisoriesCheck Version:
uname -rVerify Fix Applied:
Verify kernel version is updated to one containing fix commits, or test mmap operations on DRM objects📡 Detection & Monitoring
Log Indicators:
- Kernel oops/panic messages related to drm_gem_ttm_mmap
- System crashes during graphics operations
- Unexpected process termination with memory corruption errors
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
source="kernel" AND ("drm_gem_ttm_mmap" OR "use-after-free" OR "kernel panic")