CVE-2021-47123
📋 TL;DR
This CVE describes a double-free vulnerability in the Linux kernel's io_uring subsystem. It allows attackers with local access to potentially cause memory corruption, leading to system crashes or privilege escalation. All Linux systems using affected kernel versions with io_uring enabled are 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 →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, complete system compromise, or kernel panic causing denial of service.
Likely Case
Kernel panic leading to system crash and denial of service.
If Mitigated
Limited to denial of service if proper isolation and privilege separation are implemented.
🎯 Exploit Status
Requires local access and knowledge of io_uring subsystem. Race condition exploitation adds complexity.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in stable kernel trees (commits: 1f64f5e903b9d1d157875721e02adadc9d6f0a5d, 447c19f3b5074409c794b350b10306e1da1ef4ba)
Vendor Advisory: https://git.kernel.org/stable/c/1f64f5e903b9d1d157875721e02adadc9d6f0a5d
Restart Required: Yes
Instructions:
1. Update to latest kernel version from your distribution. 2. Apply specific patches if backporting. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable io_uring
linuxRemove io_uring module or disable at kernel compile time
echo 'blacklist io_uring' >> /etc/modprobe.d/blacklist.conf
rmmod io_uring
Restrict io_uring access
linuxUse capabilities or SELinux/AppArmor to restrict which users can use io_uring
setcap -r /usr/bin/your_app
Use appropriate SELinux/AppArmor policies
🧯 If You Can't Patch
- Implement strict user privilege separation and limit local user access
- Monitor for kernel panics and unusual system behavior, implement crash recovery mechanisms
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if io_uring is enabled: 'uname -r' and 'lsmod | grep io_uring'Check Version:
uname -rVerify Fix Applied:
Verify kernel version is patched and check for specific commit hashes in kernel source📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- OOM killer activity
- System crash/reboot logs
Network Indicators:
- None - local exploit only
SIEM Query:
source="kernel" AND ("panic" OR "Oops" OR "BUG") AND "io_uring"