CVE-2024-56558 – This CVE describes a use-after-free vulnerabili... (How to Fix)

Q: What is the severity of CVE-2024-56558?

CVE-2024-56558 has a CVSS score of 7.8 (HIGH). This CVE describes a use-after-free vulnerability in the Linux kernel's NFS server (nfsd) where improper reference counting during cache operations could trigger a kernel warning or potential crash. It affects Linux systems running NFS server functionality. The vulnerability requires local access to trigger but could lead to denial of service.

📋 TL;DR

This CVE describes a use-after-free vulnerability in the Linux kernel's NFS server (nfsd) where improper reference counting during cache operations could trigger a kernel warning or potential crash. It affects Linux systems running NFS server functionality. The vulnerability requires local access to trigger but could lead to denial of service.

💻 Affected Systems

Products:

Linux Kernel

Versions: Linux kernel versions up to 6.12.0-rc3 (specifically vulnerable in 6.12.0-rc3 as shown in trace)

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects systems with nfsd (NFS server) functionality enabled and active. Systems only using NFS client are not affected.

📦 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 or system crash leading to denial of service, potentially disrupting NFS services and affecting dependent systems.

🟠

Likely Case

Kernel warning messages in logs and potential NFS service instability, but full system crash is less likely without intentional exploitation.

🟢

If Mitigated

Minor performance impact from warning messages with no service disruption if proper kernel protections are active.

🌐 Internet-Facing: LOW - Requires local access to trigger via specific NFS operations; not directly exploitable over network.

🏢 Internal Only: MEDIUM - Local users or processes with access to NFS server operations could trigger the vulnerability, potentially causing service disruption.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: NO

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and specific knowledge of triggering the vulnerable code path through NFS operations. The vulnerability was discovered through code review and debugging, not active exploitation.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in Linux kernel commit 1cecfdbc6bfc89c516d286884c7f29267b95de2b and backported to stable branches

Vendor Advisory: https://git.kernel.org/stable/c/1cecfdbc6bfc89c516d286884c7f29267b95de2b

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing fix commit 1cecfdbc6bfc89c516d286884c7f29267b95de2b or later. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.

🔧 Temporary Workarounds

Disable NFS server

linux

Temporarily disable nfsd service if NFS server functionality is not required

systemctl stop nfs-server
systemctl disable nfs-server

Restrict access to /proc/fs/nfs/exports

linux

Limit which users can access the vulnerable interface

chmod 600 /proc/fs/nfs/exports
chown root:root /proc/fs/nfs/exports

🧯 If You Can't Patch

Disable NFS server functionality if not required
Implement strict access controls to limit which users can interact with NFS server operations

🔍 How to Verify

Check if Vulnerable:

Check kernel version and if nfsd is active: uname -r && systemctl is-active nfs-server

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version contains fix commit: grep -q '1cecfdbc6bfc89c516d286884c7f29267b95de2b' /proc/version_signature || echo 'Check kernel changelog'

📡 Detection & Monitoring

Log Indicators:

Kernel logs containing 'refcount_t: addition on 0; use-after-free'
WARNING messages from nfsd in dmesg
System crashes or instability related to NFS operations

Network Indicators:

Unusual NFS request patterns from local users
NFS service interruptions

SIEM Query:

source="kernel" AND "refcount_warn_saturate" AND "nfsd" OR source="dmesg" AND "use-after-free" AND "e_show"

📊 Metadata

CVE ID: CVE-2024-56558

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: December 27, 2024

Last Updated: November 3, 2025

🔗 References

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🔗 Related Vulnerabilities

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