CVE-2021-3715
📋 TL;DR
CVE-2021-3715 is a use-after-free vulnerability in the Linux kernel's Traffic Control subsystem that allows unprivileged local users to escalate privileges to root. This affects Linux systems with the Traffic Control subsystem enabled. The vulnerability impacts confidentiality, integrity, and system availability.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with root privileges, allowing attackers to install persistent malware, exfiltrate sensitive data, or render the system unusable.
Likely Case
Local privilege escalation leading to unauthorized access to sensitive files, system configuration changes, or lateral movement within the network.
If Mitigated
Limited impact if proper access controls, kernel hardening, and monitoring are in place, though the vulnerability still presents significant risk.
🎯 Exploit Status
Exploitation requires local access and knowledge of kernel internals. Public proof-of-concept code exists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel 5.14-rc1 and later
Vendor Advisory: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ef299cc3fa1a9e1288665a9fdc8bff55629fd359
Restart Required: Yes
Instructions:
1. Update Linux kernel to version 5.14-rc1 or later. 2. Reboot the system. 3. Verify the kernel version with 'uname -r'.
🔧 Temporary Workarounds
Disable Traffic Control subsystem
linuxDisables the vulnerable Traffic Control subsystem to prevent exploitation
echo 'blacklist sch_ingress' >> /etc/modprobe.d/blacklist.conf
rmmod sch_ingress
🧯 If You Can't Patch
- Restrict local user access to essential personnel only
- Implement strict kernel module loading restrictions and disable unnecessary kernel features
🔍 How to Verify
Check if Vulnerable:
Check kernel version with 'uname -r' and compare against affected versions (before 5.14-rc1)Check Version:
uname -rVerify Fix Applied:
Verify kernel version is 5.14-rc1 or later with 'uname -r'📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- System crash dumps
- Unusual privilege escalation attempts in audit logs
Network Indicators:
- Unusual outbound connections from compromised systems
SIEM Query:
source="kernel" AND ("panic" OR "oops" OR "use-after-free")