CVE-2025-38443 – This CVE describes a use-after-free vulnerabili... (How to Fix)

Q: What is the severity of CVE-2025-38443?

CVE-2025-38443 has a CVSS score of 7.8 (HIGH). This CVE describes a use-after-free vulnerability in the Linux kernel's NBD (Network Block Device) driver. When nbd_genl_connect() encounters certain errors after starting a device, it fails to properly stop the device, allowing freed memory to be accessed by recv_work threads. This affects Linux systems using NBD functionality.

📋 TL;DR

This CVE describes a use-after-free vulnerability in the Linux kernel's NBD (Network Block Device) driver. When nbd_genl_connect() encounters certain errors after starting a device, it fails to properly stop the device, allowing freed memory to be accessed by recv_work threads. This affects Linux systems using NBD functionality.

💻 Affected Systems

Products:

Linux kernel

Versions: Kernel versions containing the vulnerable code up to the fix commit. Specific version ranges depend on distribution backports.

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when NBD module is loaded and in use. Many systems don't use NBD 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...

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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

Kernel panic, system crash, or potential arbitrary code execution with kernel privileges leading to complete system compromise.

🟠

Likely Case

System instability, kernel panic, or denial of service causing affected NBD connections to fail.

🟢

If Mitigated

No impact if NBD functionality is disabled or the system is patched.

🌐 Internet-Facing: LOW - NBD is typically used internally or in trusted networks, not directly internet-exposed.

🏢 Internal Only: MEDIUM - Systems using NBD for storage or virtualization could experience service disruption or potential privilege escalation.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires triggering specific error conditions in NBD connection setup. The vulnerability was discovered through syzkaller fuzzing.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in kernel commit 002aca89753f666d878ca0eb8584c372684ac4ba and backported to stable branches

Vendor Advisory: https://git.kernel.org/stable/c/002aca89753f666d878ca0eb8584c372684ac4ba

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing the fix. 2. For distributions: Use package manager (apt/yum/dnf) to update kernel package. 3. Reboot system to load new kernel.

🔧 Temporary Workarounds

Disable NBD module

linux

Prevent loading of the NBD kernel module if not needed

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

Restrict NBD usage

linux

Only allow trusted users to configure NBD devices

chmod 600 /dev/nbd*
setfacl -m u:trusteduser:rw /dev/nbd*

🧯 If You Can't Patch

Disable NBD functionality entirely if not required
Monitor systems for NBD-related crashes or unusual behavior

🔍 How to Verify

Check if Vulnerable:

Check if NBD module is loaded: lsmod | grep nbd. If loaded and kernel version is before fix, system may be vulnerable.

Check Version:

uname -r

Verify Fix Applied:

Check kernel version includes fix commit: uname -r and verify with distribution's security advisory.

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
KASAN reports of use-after-free in nbd driver
System logs showing NBD connection failures

Network Indicators:

Unexpected NBD connection attempts from untrusted sources

SIEM Query:

source="kernel" AND ("nbd" OR "KASAN" OR "use-after-free")

📊 Metadata

CVE ID: CVE-2025-38443

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-416

EPSS Score: 0.02% exploit probability (4.5th percentile)

Published: July 25, 2025

Last Updated: December 22, 2025

🔗 References

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