CVE-2021-47254 – This is a use-after-free vulnerability in the L... (How to Fix)

Q: What is the severity of CVE-2021-47254?

CVE-2021-47254 has a CVSS score of 7.8 (HIGH). This is a use-after-free vulnerability in the Linux kernel's GFS2 filesystem implementation that could allow local attackers to cause denial of service or potentially execute arbitrary code. It affects systems using the GFS2 filesystem, primarily enterprise Linux servers with clustered storage configurations.

📋 TL;DR

This is a use-after-free vulnerability in the Linux kernel's GFS2 filesystem implementation that could allow local attackers to cause denial of service or potentially execute arbitrary code. It affects systems using the GFS2 filesystem, primarily enterprise Linux servers with clustered storage configurations.

💻 Affected Systems

Products:

Linux kernel with GFS2 filesystem support

Versions: Linux kernel versions before the fix commits (specific versions vary by distribution)

Operating Systems: Linux distributions with vulnerable kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if GFS2 filesystem is actually in use. Most standard Linux installations don't use GFS2 by default.

📦 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 →

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 →

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

Kernel panic leading to system crash, or potential privilege escalation to root via arbitrary code execution in kernel context.

🟠

Likely Case

System instability, kernel crashes, or denial of service affecting GFS2 filesystem operations.

🟢

If Mitigated

Limited impact if GFS2 filesystem is not in use or if proper access controls prevent local user exploitation.

🌐 Internet-Facing: LOW - Requires local access to exploit, not directly reachable via network.

🏢 Internal Only: MEDIUM - Local users or compromised services could exploit this vulnerability on affected systems.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and knowledge of GFS2 internals. No public exploits have been documented.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Linux kernel versions containing commit 0364742decb0f02bc183404868b82896f7992595 or later

Vendor Advisory: https://git.kernel.org/stable/c/0364742decb0f02bc183404868b82896f7992595

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.

🔧 Temporary Workarounds

Disable GFS2 module

linux

Prevent loading of GFS2 kernel module if not needed

echo 'install gfs2 /bin/true' >> /etc/modprobe.d/disable-gfs2.conf
rmmod gfs2

Restrict local user access

all

Limit which users can access the system to reduce attack surface

🧯 If You Can't Patch

Ensure strict access controls to prevent unauthorized local users from accessing the system
Monitor system logs for kernel panics or unusual GFS2-related errors

🔍 How to Verify

Check if Vulnerable:

Check if GFS2 module is loaded: lsmod | grep gfs2. If loaded, check kernel version against patched versions for your distribution.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version after update and ensure no kernel panics or GFS2-related crashes occur during normal operations.

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages in /var/log/messages or dmesg
GFS2-related error messages or crashes

Network Indicators:

None - local vulnerability only

SIEM Query:

source="kernel" AND ("panic" OR "Oops" OR "gfs2")

📊 Metadata

CVE ID: CVE-2021-47254

CVSS v3 Score: 7.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-416

Published: May 21, 2024

Last Updated: January 27, 2026

🔗 References

📤 Share & Export

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🔗 Related Vulnerabilities

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