CVE-2025-39808 – A null pointer dereference vulnerability in the... (How to Fix)

Q: What is the severity of CVE-2025-39808?

CVE-2025-39808 has a CVSS score of 5.5 (MEDIUM). A null pointer dereference vulnerability in the Linux kernel's HID ntrig driver allows local attackers to trigger a kernel page fault by sending crafted descriptors to /dev/uhid. This affects Linux systems with the hid-ntrig driver loaded, potentially causing denial of service. The vulnerability requires local access to the system.

📋 TL;DR

A null pointer dereference vulnerability in the Linux kernel's HID ntrig driver allows local attackers to trigger a kernel page fault by sending crafted descriptors to /dev/uhid. This affects Linux systems with the hid-ntrig driver loaded, potentially causing denial of service. The vulnerability requires local access to the system.

💻 Affected Systems

Products:

Linux kernel

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

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only vulnerable when hid-ntrig driver is loaded (typically for N-trig touchscreen devices). Systems without these devices may not have the driver loaded.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

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...

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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 →

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 denial of service causing kernel panic or system crash, requiring physical or remote console access to recover.

🟠

Likely Case

Local denial of service affecting the HID subsystem, potentially disrupting input devices until system restart.

🟢

If Mitigated

Minimal impact with proper access controls preventing unauthorized local users from accessing /dev/uhid.

🌐 Internet-Facing: LOW - Requires local access to exploit, not directly reachable from internet.

🏢 Internal Only: MEDIUM - Local attackers or malicious users with shell access could exploit this to cause denial of service.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and ability to write to /dev/uhid. No authentication bypass needed beyond local access.

🛠️ Fix & Mitigation

✅ Official Fix

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

Vendor Advisory: https://git.kernel.org/stable/c/019c34ca11372de891c06644846eb41fca7c890c

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify hid-ntrig module loads without errors.

🔧 Temporary Workarounds

Disable hid-ntrig module

Linux

Prevent loading of vulnerable driver if N-trig devices are not needed

echo 'blacklist hid-ntrig' >> /etc/modprobe.d/blacklist.conf
rmmod hid-ntrig

Restrict /dev/uhid access

Linux

Limit access to the vulnerable interface to prevent exploitation

chmod 600 /dev/uhid
chown root:root /dev/uhid

🧯 If You Can't Patch

Implement strict access controls on /dev/uhid device file
Monitor system logs for kernel panic or page fault errors related to hid-ntrig

🔍 How to Verify

Check if Vulnerable:

Check if hid-ntrig module is loaded: lsmod | grep hid_ntrig

Check Version:

uname -r

Verify Fix Applied:

Check kernel version is patched: uname -r and verify against distribution security advisories

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
Page fault errors mentioning hid_ntrig or ntrig_report_version
System crash/reboot logs

Network Indicators:

None - local exploitation only

SIEM Query:

source="kernel" AND ("page fault" OR "kernel panic") AND ("hid_ntrig" OR "ntrig")

📊 Metadata

CVE ID: CVE-2025-39808

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

EPSS Score: 0.01% exploit probability (1th percentile)

Published: September 16, 2025

Last Updated: January 16, 2026

🔗 References

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