CVE-2020-36387
📋 TL;DR
This is a use-after-free vulnerability in the Linux kernel's io_uring subsystem that allows local attackers to potentially escalate privileges or crash the system. It affects Linux systems running kernel versions before 5.8.2. The vulnerability occurs when the kernel incorrectly manages memory references in asynchronous I/O 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, or kernel panic causing denial of service.
Likely Case
Local privilege escalation allowing attackers to gain root access on affected systems.
If Mitigated
Limited impact if proper access controls restrict local user accounts and SELinux/AppArmor are properly configured.
🎯 Exploit Status
Proof-of-concept available through syzbot/syzkaller. Exploitation requires local access and knowledge of kernel exploitation techniques.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel 5.8.2 and later
Vendor Advisory: https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.8.2
Restart Required: Yes
Instructions:
1. Update Linux kernel to version 5.8.2 or later. 2. For distributions: Use package manager (apt/yum/dnf) to update kernel package. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable io_uring module
linuxPrevent loading of the vulnerable io_uring subsystem
echo 'blacklist io_uring' >> /etc/modprobe.d/blacklist.conf
rmmod io_uring
Restrict access to /dev/io_uring
linuxLimit which users can access io_uring device
chmod 600 /dev/io_uring
chown root:root /dev/io_uring
🧯 If You Can't Patch
- Implement strict access controls to limit local user accounts
- Use SELinux or AppArmor to restrict process capabilities and system access
🔍 How to Verify
Check if Vulnerable:
Check kernel version with 'uname -r' and compare to affected versions. Also check if io_uring is loaded with 'lsmod | grep io_uring'.Check Version:
uname -rVerify Fix Applied:
Verify kernel version is 5.8.2 or later with 'uname -r'. Check that system is stable and no kernel panics occur during I/O operations.📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages in /var/log/kern.log or dmesg
- Use-after-free errors in kernel logs
- Unexpected process crashes with I/O operations
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
source="kernel" AND ("use-after-free" OR "io_uring" OR "kernel panic")🔗 References
- https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.8.2
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6d816e088c359866f9867057e04f244c608c42fe
- https://security.netapp.com/advisory/ntap-20210727-0006/
- https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-io_async_task_func
- https://syzkaller.appspot.com/bug?id=ce5f07d6ec3b5050b8f0728a3b389aa510f2591b
- https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.8.2
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6d816e088c359866f9867057e04f244c608c42fe
- https://security.netapp.com/advisory/ntap-20210727-0006/
- https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-io_async_task_func
- https://syzkaller.appspot.com/bug?id=ce5f07d6ec3b5050b8f0728a3b389aa510f2591b
