CVE-2021-47416 – A memory leak vulnerability in the Linux kernel... (How to Fix)

Q: What is the severity of CVE-2021-47416?

CVE-2021-47416 has a CVSS score of 5.5 (MEDIUM). A memory leak vulnerability in the Linux kernel's MDIO bus interface occurs when device registration fails but memory isn't properly released. This affects Linux systems using MDIO bus functionality, potentially leading to resource exhaustion over time.

📋 TL;DR

A memory leak vulnerability in the Linux kernel's MDIO bus interface occurs when device registration fails but memory isn't properly released. This affects Linux systems using MDIO bus functionality, potentially leading to resource exhaustion over time.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected kernel versions not specified in CVE, but patches exist for multiple stable branches

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects systems using MDIO bus functionality for network PHY management

📦 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Sustained exploitation could cause kernel memory exhaustion leading to system instability, crashes, or denial of service.

🟠

Likely Case

Memory leak gradually consumes kernel resources, potentially causing performance degradation or system instability over extended periods.

🟢

If Mitigated

With proper monitoring and resource limits, impact is limited to potential performance issues rather than complete system failure.

🌐 Internet-Facing: LOW - This is a kernel-level memory management issue requiring local access or specific MDIO bus operations.

🏢 Internal Only: MEDIUM - Internal systems with MDIO bus usage could experience resource exhaustion affecting stability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: NO

Unauthenticated Exploit: ✅ No

Complexity: HIGH

Exploitation requires triggering specific MDIO bus registration failures, making it difficult to weaponize effectively.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Multiple stable kernel versions with fixes (see references)

Vendor Advisory: https://git.kernel.org/stable/c/064c2616234a7394867c924b5c1303974f3a4f4d

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version 2. Reboot system 3. Verify kernel version matches patched release

🔧 Temporary Workarounds

Disable MDIO bus functionality

linux

Remove or disable MDIO bus modules if not required

modprobe -r phy_mdio
echo 'blacklist phy_mdio' >> /etc/modprobe.d/blacklist.conf

🧯 If You Can't Patch

Monitor kernel memory usage for unusual growth patterns
Implement system resource limits and restart services periodically

🔍 How to Verify

Check if Vulnerable:

Check kernel version against patched releases in git.kernel.org references

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version after update matches patched release and monitor for memory leaks

📡 Detection & Monitoring

Log Indicators:

Kernel oom-killer messages
Memory allocation failures in dmesg
MDIO bus error messages

Network Indicators:

None specific - this is a local memory management issue

SIEM Query:

source="kernel" AND ("oom" OR "memory allocation failure" OR "MDIO")

📊 Metadata

CVE ID: CVE-2021-47416

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-401

Published: May 21, 2024

Last Updated: December 31, 2024

🔗 References

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🔗 Related Vulnerabilities

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