CVE-2024-40900 – A use-after-free vulnerability in the Linux ker... (How to Fix)

Q: What is the severity of CVE-2024-40900?

CVE-2024-40900 has a CVSS score of 7.8 (HIGH). A use-after-free vulnerability in the Linux kernel's cachefiles subsystem allows local attackers to potentially execute arbitrary code or cause denial of service. The vulnerability occurs when requests aren't properly removed from the xarray during flushing, leading to freed memory being accessed. This affects Linux systems with cachefiles enabled.

📋 TL;DR

A use-after-free vulnerability in the Linux kernel's cachefiles subsystem allows local attackers to potentially execute arbitrary code or cause denial of service. The vulnerability occurs when requests aren't properly removed from the xarray during flushing, leading to freed memory being accessed. This affects Linux systems with cachefiles enabled.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE, but patches exist for multiple stable branches.

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when cachefiles subsystem is enabled and in use. Many distributions don't enable this by default.

📦 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

Local privilege escalation to root, arbitrary code execution, or kernel panic leading to system crash.

🟠

Likely Case

Kernel panic causing system instability or denial of service.

🟢

If Mitigated

Limited impact if proper access controls restrict local user accounts and cachefiles isn't in use.

🌐 Internet-Facing: LOW - This is a local vulnerability requiring access to the system.

🏢 Internal Only: MEDIUM - Local users or compromised accounts could exploit this vulnerability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access and knowledge of cachefiles usage. Race condition makes exploitation timing-dependent.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Multiple stable kernel versions with commits 0fc75c5940fa, 37e19cf86a52, 50d0e55356ba, 9f13aacdd4ee

Vendor Advisory: https://git.kernel.org/stable/c/0fc75c5940fa634d84e64c93bfc388e1274ed013

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel. 3. Verify kernel version matches patched release.

🔧 Temporary Workarounds

Disable cachefiles

linux

Disable the cachefiles subsystem if not required.

echo 'blacklist cachefiles' > /etc/modprobe.d/cachefiles.conf
rmmod cachefiles

🧯 If You Can't Patch

Restrict local user access to systems where cachefiles is enabled
Monitor for unusual system crashes or kernel panics

🔍 How to Verify

Check if Vulnerable:

Check if cachefiles module is loaded: lsmod | grep cachefiles. If loaded, check kernel version against patched releases.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version includes the fix commits: uname -r and check with distribution vendor.

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
OOM killer activity
System crashes

Network Indicators:

None - local vulnerability

SIEM Query:

search 'kernel panic' OR 'system crash' OR 'segfault' in kernel logs

📊 Metadata

CVE ID: CVE-2024-40900

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

Published: July 12, 2024

Last Updated: November 3, 2025

🔗 References

📤 Share & Export

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🔗 Related Vulnerabilities

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