CVE-2025-39888 – A memory corruption vulnerability in the Linux ... (How to Fix)

Q: What is the severity of CVE-2025-39888?

CVE-2025-39888 has a CVSS score of 7.8 (HIGH). A memory corruption vulnerability in the Linux kernel's FUSE filesystem implementation allows attackers to write beyond allocated memory boundaries. This affects systems using FUSE filesystems with untrusted userspace components. The vulnerability can lead to kernel crashes or potential privilege escalation.

📋 TL;DR

A memory corruption vulnerability in the Linux kernel's FUSE filesystem implementation allows attackers to write beyond allocated memory boundaries. This affects systems using FUSE filesystems with untrusted userspace components. The vulnerability can lead to kernel crashes or potential privilege escalation.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not specified in CVE, but patches available for stable branches

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when FUSE filesystem is mounted and userspace components trigger the boundary condition

📦 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 →

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 or potential privilege escalation to root if combined with other vulnerabilities

🟠

Likely Case

Kernel crash causing system instability and denial of service

🟢

If Mitigated

Limited impact if FUSE is not used or only trusted userspace components are allowed

🌐 Internet-Facing: LOW - FUSE typically requires local access or specific mount configurations

🏢 Internal Only: MEDIUM - Local users or processes with FUSE access could trigger the vulnerability

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires ability to interact with FUSE filesystem operations and trigger specific boundary conditions

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Patches available in stable kernel trees via git commits 623719227b114d73a2cee45f1b343ced63ce09ec and 9d81ba6d49a7457784f0b6a71046818b86ec7e44

Vendor Advisory: https://git.kernel.org/stable/c/623719227b114d73a2cee45f1b343ced63ce09ec

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 FUSE filesystems

linux

Prevent mounting of FUSE filesystems to eliminate attack surface

modprobe -r fuse
echo 'blacklist fuse' >> /etc/modprobe.d/blacklist.conf

Restrict FUSE access

linux

Limit which users can mount FUSE filesystems

chmod 640 /dev/fuse
setfacl -m u:root:rw /dev/fuse

🧯 If You Can't Patch

Monitor for FUSE-related crashes in kernel logs
Restrict user access to systems where FUSE is required

🔍 How to Verify

Check if Vulnerable:

Check kernel version and compare with distribution's patched versions. Examine if FUSE is loaded: lsmod | grep fuse

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version after update and ensure no FUSE-related crashes in dmesg

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
Out of bounds write errors in dmesg
FUSE-related crash reports

Network Indicators:

Not network exploitable

SIEM Query:

source="kernel" AND ("fuse" OR "out-of-bounds" OR "slab-out-of-bounds")

📊 Metadata

CVE ID: CVE-2025-39888

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-787

EPSS Score: 0.03% exploit probability (6.3th percentile)

Published: September 23, 2025

Last Updated: January 14, 2026

🔗 References

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