CVE-2021-47343 – This CVE is an uninitialized variable vulnerabi... (How to Fix)

Q: What is the severity of CVE-2021-47343?

CVE-2021-47343 has a CVSS score of 5.5 (MEDIUM). This CVE is an uninitialized variable vulnerability in the Linux kernel's device mapper btree removal function. When removal fails due to an IO read error, an uninitialized value can be assigned to the root pointer, potentially leading to out-of-bounds memory access and system crashes. This affects Linux systems using device mapper features like dm-thin.

📋 TL;DR

This CVE is an uninitialized variable vulnerability in the Linux kernel's device mapper btree removal function. When removal fails due to an IO read error, an uninitialized value can be assigned to the root pointer, potentially leading to out-of-bounds memory access and system crashes. This affects Linux systems using device mapper features like dm-thin.

💻 Affected Systems

Products:

Linux kernel

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

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only exploitable when using device mapper features like dm-thin and encountering IO errors during btree removal operations.

📦 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel panic or system crash leading to denial of service, potentially allowing information disclosure through memory corruption.

🟠

Likely Case

System crash or kernel panic when specific device mapper operations fail due to IO errors.

🟢

If Mitigated

No impact if proper kernel patches are applied or affected device mapper features are not used.

🌐 Internet-Facing: LOW - Requires local access and specific device mapper operations.

🏢 Internal Only: MEDIUM - Local users or processes with device mapper access could trigger crashes.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: HIGH

Exploitation requires specific conditions: local access, device mapper usage, and triggering IO errors during btree removal.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions with commits 4c84b3e0728ffe10d89c633694c35a02b5c477dc or later

Vendor Advisory: https://git.kernel.org/stable/c/4c84b3e0728ffe10d89c633694c35a02b5c477dc

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel.

🔧 Temporary Workarounds

Disable device mapper features

linux

Avoid using dm-thin and other device mapper features that trigger the vulnerable code path

🧯 If You Can't Patch

Monitor system logs for device mapper errors and kernel panics
Restrict local user access to device mapper operations

🔍 How to Verify

Check if Vulnerable:

Check kernel version and compare with distribution's patched versions. Vulnerable if using unpatched kernel with device mapper features.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is updated to include the fix commits. Check /proc/version or uname -r.

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
General protection fault errors
Device mapper error logs

SIEM Query:

source="kernel" AND ("general protection fault" OR "dm_btree_remove" OR "device mapper" AND error)

📊 Metadata

CVE ID: CVE-2021-47343

CVSS v3 Score: 5.5 (MEDIUM)

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

CWE: CWE-1188

Published: May 21, 2024

Last Updated: May 12, 2025

🔗 References

📤 Share & Export

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🔗 Related Vulnerabilities

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