CVE-2023-52856 – This CVE describes a NULL pointer dereference v... (How to Fix)

Q: What is the severity of CVE-2023-52856?

CVE-2023-52856 has a CVSS score of 5.5 (MEDIUM). This CVE describes a NULL pointer dereference vulnerability in the Linux kernel's lt8912b display bridge driver. When the bridge detaches (e.g., during module removal or device disconnection), improper cleanup calls cause a kernel crash, leading to denial of service. Systems using affected Linux kernel versions with the lt8912b driver loaded are vulnerable.

📋 TL;DR

This CVE describes a NULL pointer dereference vulnerability in the Linux kernel's lt8912b display bridge driver. When the bridge detaches (e.g., during module removal or device disconnection), improper cleanup calls cause a kernel crash, leading to denial of service. Systems using affected Linux kernel versions with the lt8912b driver loaded are vulnerable.

💻 Affected Systems

Products:

Linux kernel

Versions: Kernel versions containing the vulnerable lt8912b driver code before the fix commits. Specific affected versions depend on distribution backports.

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if the lontium_lt8912b kernel module is loaded (typically when using LT8912B display bridge hardware). Most systems won't have this loaded 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel panic leading to complete system crash and denial of service, requiring physical or remote reboot.

🟠

Likely Case

System crash when removing the lt8912b module or disconnecting the display bridge hardware, causing temporary service disruption.

🟢

If Mitigated

No impact if the lt8912b driver is not loaded or the vulnerable code path is not triggered.

🌐 Internet-Facing: LOW - This is a local kernel driver issue requiring driver interaction, not directly exploitable over network.

🏢 Internal Only: MEDIUM - Local users or processes with sufficient privileges to load/unload kernel modules can trigger the crash.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: NO

Unauthenticated Exploit: ✅ No

Complexity: LOW - Requires ability to trigger bridge detach (e.g., via rmmod or hardware disconnection).

Exploitation requires kernel module loading/unloading privileges or physical access to trigger hardware events.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in kernel commits: 42071feab712, 44283993144a, 7bf0cb8f4028, b65e3249f3ca, fcd9895e3654

Vendor Advisory: https://git.kernel.org/stable/c/42071feab712ba2a139b8928f7e0f8d3a6fc719e

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix commits. 2. For distributions: Apply security updates via package manager (e.g., apt upgrade linux-image). 3. Reboot to load patched kernel.

🔧 Temporary Workarounds

Unload vulnerable module

linux

Remove the lt8912b kernel module if not needed

sudo rmmod lontium_lt8912b

Blacklist module

linux

Prevent automatic loading of vulnerable module

echo 'blacklist lontium_lt8912b' | sudo tee /etc/modprobe.d/blacklist-lt8912b.conf

🧯 If You Can't Patch

Ensure only trusted users have CAP_SYS_MODULE capability to prevent module manipulation
Monitor for kernel panic events and investigate any lt8912b module unloading activities

🔍 How to Verify

Check if Vulnerable:

Check if lt8912b module is loaded: lsmod | grep lontium_lt8912b

Check Version:

uname -r

Verify Fix Applied:

Check kernel version includes fix commits: uname -r and verify with distribution security advisories

📡 Detection & Monitoring

Log Indicators:

Kernel panic/Oops messages mentioning lt8912_bridge_detach or drm_connector_cleanup
System crash/reboot events after display hardware changes

Network Indicators:

None - local vulnerability only

SIEM Query:

source="kernel" AND ("lt8912" OR "drm_connector_cleanup" OR "NULL pointer dereference")

📊 Metadata

CVE ID: CVE-2023-52856

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-476

Published: May 21, 2024

Last Updated: January 31, 2025

🔗 References

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🔗 Related Vulnerabilities

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