CVE-2025-39846 – This CVE describes a NULL pointer dereference v... (How to Fix)

Q: What is the severity of CVE-2025-39846?

CVE-2025-39846 has a CVSS score of 5.5 (MEDIUM). This CVE describes a NULL pointer dereference vulnerability in the Linux kernel's PCMCIA subsystem. If exploited, it could cause a kernel panic or system crash, affecting systems with PCMCIA hardware or drivers loaded. The vulnerability requires local access to trigger.

📋 TL;DR

This CVE describes a NULL pointer dereference vulnerability in the Linux kernel's PCMCIA subsystem. If exploited, it could cause a kernel panic or system crash, affecting systems with PCMCIA hardware or drivers loaded. The vulnerability requires local access to trigger.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not specified in CVE description; check kernel commit history for exact range

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects systems with PCMCIA hardware or PCMCIA drivers loaded. Many modern systems may not have PCMCIA hardware.

📦 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...

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 denial of service, potentially requiring physical reboot of affected systems.

🟠

Likely Case

System crash or instability when PCMCIA operations are performed, resulting in temporary unavailability.

🟢

If Mitigated

Minimal impact with proper access controls preventing unauthorized local users from triggering the vulnerability.

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

🏢 Internal Only: MEDIUM - Local users or processes could trigger the vulnerability, potentially causing system instability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access and ability to trigger PCMCIA operations. Exploitation depends on specific hardware/driver configuration.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions with commits 2ee32c4c4f636e474cd8ab7c19a68cf36072ea93 or later

Vendor Advisory: https://git.kernel.org/stable/c/2ee32c4c4f636e474cd8ab7c19a68cf36072ea93

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from distribution vendor. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.

🔧 Temporary Workarounds

Disable PCMCIA subsystem

Linux

Remove or blacklist PCMCIA kernel modules if PCMCIA hardware is not needed

echo 'blacklist pcmcia' >> /etc/modprobe.d/blacklist.conf
rmmod pcmcia_core pcmcia

🧯 If You Can't Patch

Restrict local user access to systems with PCMCIA hardware
Implement strict privilege separation to prevent unauthorized users from accessing PCMCIA operations

🔍 How to Verify

Check if Vulnerable:

Check kernel version and verify if PCMCIA modules are loaded: lsmod | grep pcmcia

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is patched and check dmesg for PCMCIA-related errors after attempting operations

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages in /var/log/messages or dmesg
NULL pointer dereference errors related to PCMCIA

Network Indicators:

None - local vulnerability only

SIEM Query:

source="kernel" AND "NULL pointer dereference" AND "pcmcia" OR "PCMCIA"

📊 Metadata

CVE ID: CVE-2025-39846

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: 0.02% exploit probability (5.1th percentile)

Published: September 19, 2025

Last Updated: January 20, 2026

🔗 References

https://git.kernel.org/stable/c/2ee32c4c4f636e474cd8ab7c19a68cf36072ea93 Patch
https://git.kernel.org/stable/c/44822df89e8f3386871d9cad563ece8e2fd8f0e7 Patch
https://git.kernel.org/stable/c/4bd570f494124608a0696da070f00236a96fb610 Patch
https://git.kernel.org/stable/c/5ff2826c998370bf7f9ae26fe802140d220e3510 Patch
https://git.kernel.org/stable/c/b990c8c6ff50649ad3352507398e443b1e3527b2 Patch
https://git.kernel.org/stable/c/ce3b7766276894d2fbb07e2047a171f9deb965de Patch
https://git.kernel.org/stable/c/d7286005e8fde0a430dc180a9f46c088c7d74483 Patch
https://git.kernel.org/stable/c/fafa7450075f41d232bc785a4ebcbf16374f2076 Patch
https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html Third Party Advisory,Mailing List
https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html Third Party Advisory,Mailing List

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

If you're affected by CVE-2025-39846, you might also want to check these: