CVE-2022-4744 – A double-free vulnerability in the Linux kernel... (How to Fix)

Q: What is the severity of CVE-2022-4744?

CVE-2022-4744 has a CVSS score of 7.8 (HIGH). A double-free vulnerability in the Linux kernel's TUN/TAP device driver allows local attackers to crash the system or potentially escalate privileges. This occurs when the register_netdevice function fails during device registration. Only systems with TUN/TAP functionality enabled are affected.

📋 TL;DR

A double-free vulnerability in the Linux kernel's TUN/TAP device driver allows local attackers to crash the system or potentially escalate privileges. This occurs when the register_netdevice function fails during device registration. Only systems with TUN/TAP functionality enabled are affected.

💻 Affected Systems

Products:

Linux kernel

Versions: Kernel versions before commit 158b515f703e (introduced in v5.19, fixed in v6.1 and backported to stable branches)

Operating Systems: Linux distributions using vulnerable kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Requires TUN/TAP device driver functionality to be enabled/loaded. Many distributions enable this by default for VPN/virtualization features.

📦 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 →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Local privilege escalation to root, complete system compromise, or kernel panic causing system crash.

🟠

Likely Case

Kernel panic leading to system crash and denial of service.

🟢

If Mitigated

Limited impact if proper access controls restrict local user privileges and TUN/TAP usage.

🌐 Internet-Facing: LOW - Requires local access to exploit, not remotely exploitable.

🏢 Internal Only: HIGH - Local users can exploit this vulnerability to gain elevated privileges or crash systems.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploit requires local access and knowledge of kernel exploitation techniques. Proof-of-concept code has been published.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions including commit 158b515f703e (v6.1+ and backported to stable branches)

Vendor Advisory: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=158b515f703e

Restart Required: Yes

Instructions:

1. Update kernel package using distribution's package manager (apt/yum/dnf). 2. Reboot system to load patched kernel. 3. Verify kernel version after reboot.

🔧 Temporary Workarounds

Disable TUN/TAP module

linux

Prevent loading of vulnerable TUN/TAP kernel module

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

Restrict device access

linux

Limit access to /dev/net/tun device file

chmod 600 /dev/net/tun
chown root:root /dev/net/tun

🧯 If You Can't Patch

Restrict local user access and privileges to minimize attack surface
Implement strict access controls on /dev/net/tun device

🔍 How to Verify

Check if Vulnerable:

Check kernel version: uname -r and compare against patched versions. Check if TUN module is loaded: lsmod | grep tun

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version after update and reboot. Confirm TUN module functions correctly for legitimate applications.

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages in /var/log/messages or dmesg
Multiple failed TUN/TAP device registration attempts

Network Indicators:

Sudden loss of VPN/tunneling connections if TUN disabled

SIEM Query:

source="kernel" AND ("panic" OR "Oops" OR "double free")

📊 Metadata

CVE ID: CVE-2022-4744

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-460

Published: March 30, 2023

Last Updated: February 14, 2025

🔗 References

http://packetstormsecurity.com/files/171912/CentOS-Stream-9-Missing-Kernel-Security-Fix.html Third Party Advisory,VDB Entry
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=158b515f703e Vendor Advisory
https://lists.debian.org/debian-lts-announce/2023/05/msg00006.html Mailing List,Third Party Advisory
https://security.netapp.com/advisory/ntap-20230526-0009/ Third Party Advisory
http://packetstormsecurity.com/files/171912/CentOS-Stream-9-Missing-Kernel-Security-Fix.html Third Party Advisory,VDB Entry
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=158b515f703e Vendor Advisory
https://lists.debian.org/debian-lts-announce/2023/05/msg00006.html Mailing List,Third Party Advisory
https://security.netapp.com/advisory/ntap-20230526-0009/ Third Party Advisory

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