CVE-2025-39772 – A NULL pointer dereference vulnerability in the... (How to Fix)

Q: What is the severity of CVE-2025-39772?

CVE-2025-39772 has a CVSS score of 5.5 (MEDIUM). A NULL pointer dereference vulnerability in the Linux kernel's hibmc DRM driver occurs when the driver fails to load properly. This can cause kernel crashes or system instability when accessing uninitialized mutexes. Systems using affected Linux kernel versions with hibmc DRM driver enabled are vulnerable.

📋 TL;DR

A NULL pointer dereference vulnerability in the Linux kernel's hibmc DRM driver occurs when the driver fails to load properly. This can cause kernel crashes or system instability when accessing uninitialized mutexes. Systems using affected Linux kernel versions with hibmc DRM driver enabled are vulnerable.

💻 Affected Systems

Products:

Linux kernel with hibmc DRM driver

Versions: Specific affected kernel versions not specified in CVE, but patches exist in stable kernel trees.

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when hibmc DRM driver is enabled and fails to load. Most systems don't use this specific driver by default.

📦 What is this software?

Debian Linux by Debian

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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...

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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

Kernel panic leading to system crash and denial of service, potentially requiring physical access to reboot.

🟠

Likely Case

System instability or crash when hibmc driver fails to load, requiring reboot to restore functionality.

🟢

If Mitigated

No impact if driver loads successfully or if hibmc functionality is not used.

🌐 Internet-Facing: LOW - Requires local access or ability to trigger driver load failure.

🏢 Internal Only: MEDIUM - Local users or processes could potentially trigger the condition leading to system instability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires ability to trigger hibmc driver load failure. Likely requires local access or specific hardware conditions.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Patched in stable kernel trees via commits referenced in CVE

Vendor Advisory: https://git.kernel.org/stable/c/93a08f856fcc5aaeeecad01f71bef3088588216a

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel. 3. Verify hibmc driver loads without errors.

🔧 Temporary Workarounds

Disable hibmc DRM driver

Linux

Prevent loading of vulnerable hibmc driver module

echo 'blacklist hibmc' > /etc/modprobe.d/disable-hibmc.conf
rmmod hibmc 2>/dev/null || true

🧯 If You Can't Patch

Ensure hibmc driver loads successfully by verifying hardware compatibility
Monitor system logs for hibmc driver failures and restart affected services

🔍 How to Verify

Check if Vulnerable:

Check if hibmc module is loaded: lsmod | grep hibmc. Check kernel version: uname -r and compare with patched versions.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is updated and check dmesg for hibmc driver loading without NULL pointer errors.

📡 Detection & Monitoring

Log Indicators:

Kernel NULL pointer dereference messages in dmesg
hibmc driver failure messages
Kernel oops or panic logs

Network Indicators:

None - local vulnerability only

SIEM Query:

source="kernel" AND ("NULL pointer" OR "hibmc" OR "oops")

📊 Metadata

CVE ID: CVE-2025-39772

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

EPSS Score: 0.01% exploit probability (1.2th percentile)

Published: September 11, 2025

Last Updated: January 16, 2026

🔗 References

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