CVE-2023-4921
📋 TL;DR
This CVE describes a use-after-free vulnerability in the Linux kernel's qfq scheduler component that allows local attackers to escalate privileges. The vulnerability occurs when the plug qdisc is configured as a class of the qfq qdisc, triggering memory corruption during packet processing. Systems running vulnerable Linux kernel versions with specific qdisc configurations are affected.
💻 Affected Systems
- Linux Kernel
📦 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 →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 attacker gains root privileges, leading to complete system compromise, data theft, and persistent backdoor installation.
Likely Case
Local user escalates to root privileges, enabling unauthorized access to sensitive data and system resources.
If Mitigated
Attack fails due to proper kernel hardening, SELinux/apparmor policies, or lack of required qdisc configuration.
🎯 Exploit Status
Requires local access and specific qdisc configuration. Exploit development requires kernel expertise.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel with commit 8fc134fee27f2263988ae38920bc03da416b03d8
Vendor Advisory: https://lists.debian.org/debian-lts-announce/2023/10/msg00027.html
Restart Required: Yes
Instructions:
1. Update kernel package using distribution's package manager. 2. For Debian/Ubuntu: apt update && apt upgrade linux-image-*. 3. For RHEL/CentOS: yum update kernel. 4. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable qfq qdisc configuration
linuxRemove or reconfigure network interfaces to not use qfq qdisc with plug qdisc as class
tc qdisc del dev eth0 root
tc qdisc add dev eth0 root fq_codel
🧯 If You Can't Patch
- Implement strict access controls to limit local user accounts
- Use kernel hardening features like SELinux/apparmor with strict policies
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if commit 8fc134fee27f is present: uname -r && git log --oneline | grep 8fc134fee27fCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes the fix: uname -r and check with distribution's security advisory📡 Detection & Monitoring
Log Indicators:
- Kernel oops messages
- System crashes
- Unexpected privilege escalation in audit logs
Network Indicators:
- Unusual network configuration changes
SIEM Query:
source="kernel" AND ("qfq" OR "use-after-free" OR "general protection fault")🔗 References
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8fc134fee27f2263988ae38920bc03da416b03d8
- https://kernel.dance/8fc134fee27f2263988ae38920bc03da416b03d8
- https://lists.debian.org/debian-lts-announce/2023/10/msg00027.html
- https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8fc134fee27f2263988ae38920bc03da416b03d8
- https://kernel.dance/8fc134fee27f2263988ae38920bc03da416b03d8
- https://lists.debian.org/debian-lts-announce/2023/10/msg00027.html
- https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html
