CVE-2024-56640 – This CVE describes a use-after-free vulnerabili... (How to Fix)

Q: What is the severity of CVE-2024-56640?

CVE-2024-56640 has a CVSS score of 7.8 (HIGH). This CVE describes a use-after-free vulnerability in the Linux kernel's SMC (Shared Memory Communications) networking subsystem. It allows attackers to potentially crash the kernel or execute arbitrary code by exploiting improper reference counting that leads to premature resource deallocation. Systems running vulnerable Linux kernel versions with SMC enabled are affected.

📋 TL;DR

This CVE describes a use-after-free vulnerability in the Linux kernel's SMC (Shared Memory Communications) networking subsystem. It allows attackers to potentially crash the kernel or execute arbitrary code by exploiting improper reference counting that leads to premature resource deallocation. Systems running vulnerable Linux kernel versions with SMC enabled are affected.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not explicitly stated in CVE, but references indicate stable kernel patches from 0cf598548a6c to f502a88fdd41

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Requires SMC subsystem to be enabled and used. Not all Linux configurations use SMC 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

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

🟠

Likely Case

Kernel crash causing denial of service, system instability, or data corruption in affected network connections.

🟢

If Mitigated

Limited impact if SMC is disabled or systems are isolated from untrusted networks.

🌐 Internet-Facing: MEDIUM - Requires network access to SMC services, but exploitation complexity is moderate.

🏢 Internal Only: MEDIUM - Internal attackers could exploit if they have network access to vulnerable systems.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires triggering specific race conditions in SMC connection handling. No public exploit code is known at this time.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits 0cf598548a6c36d90681d53c6b77d52363f2f295 or later fixes

Vendor Advisory: https://git.kernel.org/stable/c/0cf598548a6c36d90681d53c6b77d52363f2f295

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution vendor. 2. Reboot system to load new kernel. 3. Verify kernel version with 'uname -r'.

🔧 Temporary Workarounds

Disable SMC module

linux

Prevent loading of SMC kernel module to mitigate vulnerability

echo 'install smc /bin/false' >> /etc/modprobe.d/disable-smc.conf
rmmod smc 2>/dev/null || true

Blacklist SMC module

linux

Blacklist SMC module to prevent automatic loading

echo 'blacklist smc' >> /etc/modprobe.d/blacklist-smc.conf

🧯 If You Can't Patch

Restrict network access to systems using SMC protocol
Monitor kernel logs for refcount warnings related to SMC

🔍 How to Verify

Check if Vulnerable:

Check if SMC module is loaded: 'lsmod | grep smc'. If loaded and kernel version is unpatched, system is vulnerable.

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is patched and check dmesg for absence of refcount warnings related to SMC.

📡 Detection & Monitoring

Log Indicators:

Kernel logs showing 'refcount_t: addition on 0; use-after-free' or 'refcount_t: underflow; use-after-free' with SMC stack traces
System crashes or instability when SMC connections are active

Network Indicators:

Unusual SMC protocol traffic patterns
Connection attempts to SMC ports (typically 3260)

SIEM Query:

source="kernel" AND ("refcount_t" AND "use-after-free" AND "smc")

📊 Metadata

CVE ID: CVE-2024-56640

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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