CVE-2021-20226
📋 TL;DR
A use-after-free vulnerability in Linux kernel's io_uring subsystem allows local attackers with user privileges to cause denial of service or potentially escalate privileges. This affects Linux systems with vulnerable kernel versions where io_uring is enabled. The flaw occurs when file reference counters aren't properly incremented during operations.
💻 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, data corruption, or persistent denial of service.
Likely Case
Local denial of service causing kernel panic or system crash, potentially leading to data loss.
If Mitigated
Limited impact with proper access controls and kernel hardening, though DoS risk remains for legitimate users.
🎯 Exploit Status
Exploitation requires local user access. Proof-of-concept code has been published demonstrating DoS capability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel 5.10.14 and later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1873476
Restart Required: Yes
Instructions:
1. Update kernel to version 5.10.14 or later. 2. For Red Hat/CentOS: Apply security update via yum update kernel. 3. For Ubuntu/Debian: apt update && apt upgrade linux-image. 4. Reboot system after update.
🔧 Temporary Workarounds
Disable io_uring
linuxDisable the io_uring subsystem at kernel boot
Add 'io_uring.disabled=1' to kernel boot parameters in /etc/default/grub or bootloader config
Restrict user access
allLimit local user accounts and implement strict access controls
🧯 If You Can't Patch
- Implement strict access controls to limit local user accounts
- Monitor systems for unusual crashes or kernel panics
- Consider disabling io_uring via kernel parameter if not required
🔍 How to Verify
Check if Vulnerable:
Check kernel version: uname -r. If between 5.6 and 5.10.13, system is vulnerable.Check Version:
uname -rVerify Fix Applied:
Verify kernel version is 5.10.14 or later: uname -r📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- System crash dumps
- Unexpected system reboots in syslog
Network Indicators:
- None - local exploit only
SIEM Query:
source="kernel" AND ("panic" OR "Oops" OR "BUG") AND NOT expected_crash_pattern