CVE-2021-47520 – This is a use-after-free vulnerability in the L... (How to Fix)

Q: What is the severity of CVE-2021-47520?

CVE-2021-47520 has a CVSS score of 7.8 (HIGH). This is a use-after-free vulnerability in the Linux kernel's CAN (Controller Area Network) subsystem affecting the pch_can driver. It allows attackers with local access to potentially crash the system or execute arbitrary code by exploiting memory corruption after network packet processing. Systems using the pch_can driver for CAN bus communication are affected.

📋 TL;DR

This is a use-after-free vulnerability in the Linux kernel's CAN (Controller Area Network) subsystem affecting the pch_can driver. It allows attackers with local access to potentially crash the system or execute arbitrary code by exploiting memory corruption after network packet processing. Systems using the pch_can driver for CAN bus communication are affected.

💻 Affected Systems

Products:

Linux kernel with pch_can driver enabled

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

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if pch_can driver is loaded and used (typically for Intel EG20T PCH CAN controllers). Most systems don't use this driver 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...

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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

Local privilege escalation to kernel-level code execution, potentially leading to full system compromise and persistence.

🟠

Likely Case

Kernel panic or system crash causing denial of service, potentially requiring physical access to restart.

🟢

If Mitigated

Limited to denial of service if exploit attempts are detected and blocked by security controls.

🌐 Internet-Facing: LOW - Requires local access to the system; not directly exploitable over network.

🏢 Internal Only: MEDIUM - Local attackers or malicious insiders could exploit this to gain elevated privileges or cause system instability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access and knowledge of kernel exploitation techniques. No public exploits known as of analysis.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in kernel commits: 3a3c46e2eff0577454860a203be1a8295f4acb76, 3e193ef4e0a3f5bf92ede83ef214cb09d01b00aa, 6c73fc931658d8cbc8a1714b326cb31eb71d16a7, 703dde112021c93d6e89443c070e7dbd4dea612e, 94cddf1e9227a171b27292509d59691819c458db

Vendor Advisory: https://git.kernel.org/stable/c/94cddf1e9227a171b27292509d59691819c458db

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix commits. 2. Check your distribution's security advisories for specific patched versions. 3. Reboot system after kernel update.

🔧 Temporary Workarounds

Disable pch_can driver

linux

Prevent loading of the vulnerable driver module

echo 'blacklist pch_can' >> /etc/modprobe.d/blacklist.conf
rmmod pch_can

🧯 If You Can't Patch

Restrict local access to systems using pch_can driver
Implement kernel hardening measures like SELinux/AppArmor to limit impact

🔍 How to Verify

Check if Vulnerable:

Check if pch_can module is loaded: lsmod | grep pch_can. Check kernel version against patched versions.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version includes fix commits. Check that pch_can module functions normally after update.

📡 Detection & Monitoring

Log Indicators:

Kernel oops messages
System crashes/panics
CAN subsystem errors in dmesg

Network Indicators:

Unusual CAN bus traffic patterns

SIEM Query:

Search for kernel panic events or module loading failures related to pch_can

📊 Metadata

CVE ID: CVE-2021-47520

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 24, 2024

Last Updated: November 21, 2024

🔗 References

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🔗 Related Vulnerabilities

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