CVE-2024-40909 – This CVE describes a use-after-free vulnerabili... (How to Fix)

Q: What is the severity of CVE-2024-40909?

CVE-2024-40909 has a CVSS score of 7.8 (HIGH). This CVE describes a use-after-free vulnerability in the Linux kernel's BPF subsystem. The flaw occurs when freeing BPF links, potentially allowing attackers to execute arbitrary code or crash the system. It affects systems running vulnerable Linux kernel versions with BPF functionality enabled.

📋 TL;DR

This CVE describes a use-after-free vulnerability in the Linux kernel's BPF subsystem. The flaw occurs when freeing BPF links, potentially allowing attackers to execute arbitrary code or crash the system. It affects systems running vulnerable Linux kernel versions with BPF functionality enabled.

💻 Affected Systems

Products:

Linux Kernel

Versions: Specific vulnerable versions not explicitly stated in CVE description, but references indicate stable kernel patches

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Requires BPF functionality to be enabled/available. Most modern Linux distributions have BPF enabled 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel privilege escalation leading to full system compromise, arbitrary code execution at kernel level, or complete system crash/DoS.

🟠

Likely Case

Kernel panic leading to system crash and denial of service, potentially requiring physical access or reboot to restore functionality.

🟢

If Mitigated

Limited impact if BPF functionality is disabled or systems are properly patched.

🌐 Internet-Facing: MEDIUM - Requires local access or ability to execute code on the system, but could be chained with other vulnerabilities.

🏢 Internal Only: HIGH - Local attackers or malicious users could exploit this to gain kernel privileges or crash systems.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access to trigger the use-after-free condition. Syzbot reported the issue, suggesting it was found through fuzzing.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits: 2884dc7d08d98a89d8d65121524bb7533183a63a, 91cff53136daeff50816b0baeafd38a6976f6209, fa97b8fed9896f1e89cb657513e483a152d4c382

Vendor Advisory: https://git.kernel.org/stable/c/2884dc7d08d98a89d8d65121524bb7533183a63a

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 kernel version after reboot.

🔧 Temporary Workarounds

Disable BPF functionality

linux

Disable BPF subsystem to prevent exploitation of this vulnerability

echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
Remove BPF kernel modules if loaded

🧯 If You Can't Patch

Restrict user access to systems to prevent local exploitation
Implement strict privilege separation and limit users who can execute BPF programs

🔍 How to Verify

Check if Vulnerable:

Check kernel version and compare with patched versions from distribution vendor. Check if BPF is enabled: lsmod | grep bpf

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version after update matches patched version. Check system logs for successful boot with new kernel.

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
OOPs (Out of memory) errors in kernel logs
System crash/reboot events

Network Indicators:

None - local vulnerability only

SIEM Query:

source="kernel" AND ("panic" OR "Oops" OR "use-after-free" OR "bpf_link")

📊 Metadata

CVE ID: CVE-2024-40909

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 21, 2024

🔗 References

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🔗 Related Vulnerabilities

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