CVE-2023-51781 – This CVE describes a use-after-free vulnerabili... (How to Fix)

Q: What is the severity of CVE-2023-51781?

CVE-2023-51781 has a CVSS score of 7.0 (HIGH). This CVE describes a use-after-free vulnerability in the Linux kernel's AppleTalk protocol implementation. Attackers can exploit a race condition in atalk_recvmsg to cause memory corruption, potentially leading to privilege escalation or system crashes. Systems running Linux kernels before version 6.6.8 with AppleTalk support are affected.

📋 TL;DR

This CVE describes a use-after-free vulnerability in the Linux kernel's AppleTalk protocol implementation. Attackers can exploit a race condition in atalk_recvmsg to cause memory corruption, potentially leading to privilege escalation or system crashes. Systems running Linux kernels before version 6.6.8 with AppleTalk support are affected.

💻 Affected Systems

Products:

Linux kernel

Versions: All versions before 6.6.8

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if AppleTalk (CONFIG_ATALK) is enabled in kernel configuration. Most modern distributions disable AppleTalk by default.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

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...

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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 →

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, kernel panic causing denial of service, or arbitrary code execution in kernel context.

🟠

Likely Case

Kernel panic leading to system crash/reboot or local privilege escalation if successfully exploited.

🟢

If Mitigated

Minimal impact if AppleTalk is disabled or systems are patched; potential denial of service if exploited.

🌐 Internet-Facing: LOW (AppleTalk is legacy protocol rarely exposed externally)

🏢 Internal Only: MEDIUM (requires local access or internal network position to exploit)

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access to trigger the race condition. Exploitation requires precise timing and knowledge of kernel memory layout.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Linux kernel 6.6.8 and later

Vendor Advisory: https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.6.8

Restart Required: Yes

Instructions:

1. Update kernel to version 6.6.8 or later. 2. For distributions: Use package manager (apt/yum/dnf) to install latest kernel updates. 3. Reboot system to load patched kernel.

🔧 Temporary Workarounds

Disable AppleTalk module

linux

Remove or blacklist AppleTalk kernel module to eliminate attack surface

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

Prevent module loading

linux

Prevent AppleTalk module from being loaded at boot

echo 'install appletalk /bin/false' >> /etc/modprobe.d/disable-appletalk.conf

🧯 If You Can't Patch

Disable AppleTalk kernel module if not needed
Implement strict access controls to limit local user privileges

🔍 How to Verify

Check if Vulnerable:

Check kernel version and if AppleTalk module is loaded: uname -r && lsmod | grep appletalk

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is 6.6.8 or later: uname -r

📡 Detection & Monitoring

Log Indicators:

Kernel oops messages
System crashes/reboots
dmesg errors related to appletalk or general protection faults

Network Indicators:

Unusual AppleTalk protocol traffic (rare on modern networks)

SIEM Query:

source="kernel" AND ("appletalk" OR "general protection fault" OR "kernel oops")

📊 Metadata

CVE ID: CVE-2023-51781

CVSS v3 Score: 7.0 (HIGH)

CVSS Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-416

Published: January 11, 2024

Last Updated: November 21, 2024

🔗 References

https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.6.8 Release Notes
https://github.com/torvalds/linux/commit/189ff16722ee36ced4d2a2469d4ab65a8fee4198 Patch
https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2024/01/msg00005.html Mailing List,Third Party Advisory
https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.6.8 Release Notes
https://github.com/torvalds/linux/commit/189ff16722ee36ced4d2a2469d4ab65a8fee4198 Patch
https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2024/01/msg00005.html Mailing List,Third Party Advisory

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