CVE-2021-47267 – A NULL pointer dereference vulnerability in the... (How to Fix)

Q: What is the severity of CVE-2021-47267?

CVE-2021-47267 has a CVSS score of 6.3 (MEDIUM). A NULL pointer dereference vulnerability in the Linux kernel USB gadget subsystem causes kernel panics when USB 3.1 (10Gbps) devices are connected to systems with vulnerable gadget drivers. This affects Linux systems using USB gadget functionality, particularly embedded devices and systems configured as USB peripherals. The vulnerability is triggered automatically when hardware conditions are met.

📋 TL;DR

A NULL pointer dereference vulnerability in the Linux kernel USB gadget subsystem causes kernel panics when USB 3.1 (10Gbps) devices are connected to systems with vulnerable gadget drivers. This affects Linux systems using USB gadget functionality, particularly embedded devices and systems configured as USB peripherals. The vulnerability is triggered automatically when hardware conditions are met.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific vulnerable kernel versions not specified in CVE, but affects versions before the fix commits listed in references.

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects systems with USB gadget drivers that call usb_assign_descriptors() without providing super-speed-plus descriptor. Requires USB 3.1 (10Gbps) capable hardware connection.

📦 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

Kernel panic leading to system crash and denial of service, requiring physical reboot of affected device.

🟠

Likely Case

System crash when USB 3.1 (10Gbps) capable hardware is connected to vulnerable gadget configurations.

🟢

If Mitigated

No impact if USB gadget functionality is disabled or systems are patched.

🌐 Internet-Facing: LOW - Requires physical USB connection or USB-over-IP with specific hardware conditions.

🏢 Internal Only: MEDIUM - Could affect internal devices with USB gadget functionality when connected to 10Gbps USB hardware.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: NO

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires physical access to USB port or USB-over-IP capability with 10Gbps hardware. Triggered automatically when conditions are met.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits: 032e288097a553db5653af552dd8035cd2a0ba96, 45f9a2fe737dc0a5df270787f2231aee8985cd59, 5ef23506695b01d5d56a13a092a97f2478069d75, 70cd19cb5bd94bbb5bacfc9c1e4ee0071699a604, b972eff874637402ddc4a7dd11fb22538a0b6d28

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

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix commits. 2. Reboot system to load new kernel. 3. For embedded systems, update firmware with patched kernel.

🔧 Temporary Workarounds

Disable USB gadget functionality

linux

Remove or disable USB gadget drivers if not needed

modprobe -r g_ether
modprobe -r g_mass_storage
modprobe -r [specific_gadget_driver]

Limit USB speed to 5Gbps

linux

Configure gadget drivers to maximum speed of 5Gbps instead of default maximum

echo 5 > /sys/class/udc/[udc_name]/maximum_speed

🧯 If You Can't Patch

Disable USB gadget functionality entirely if not required
Physically restrict access to USB ports or use USB speed limiters

🔍 How to Verify

Check if Vulnerable:

Check if system uses USB gadget drivers and has kernel version before fix commits. Use: lsmod | grep '^g_' and uname -r

Check Version:

uname -r

Verify Fix Applied:

Check kernel version includes fix commits: git log --oneline | grep -E '032e288097a5|45f9a2fe737d|5ef23506695b|70cd19cb5bd9|b972eff87463'

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages in dmesg or system logs
NULL pointer dereference errors mentioning usb_assign_descriptors

Network Indicators:

Sudden loss of connectivity from USB gadget devices

SIEM Query:

source="kernel" AND ("panic" OR "NULL pointer dereference") AND "usb"

📊 Metadata

CVE ID: CVE-2021-47267

CVSS v3 Score: 6.3 (MEDIUM)

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

CWE: CWE-476

Published: May 21, 2024

Last Updated: April 4, 2025

🔗 References

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🔗 Related Vulnerabilities

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