CVE-2025-21700
📋 TL;DR
This Linux kernel vulnerability allows a local attacker to trigger a use-after-free condition in the traffic control subsystem by manipulating qdisc configurations, potentially leading to privilege escalation. It affects Linux systems where traffic control (tc) commands can be executed, typically requiring local access.
💻 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 privilege escalation to root, kernel panic leading to denial of service, or arbitrary code execution in kernel context.
Likely Case
Kernel crash/panic causing system instability or denial of service, potentially allowing privilege escalation in specific configurations.
If Mitigated
No impact if traffic control subsystem is not used or if user lacks CAP_NET_ADMIN capabilities.
🎯 Exploit Status
Exploit requires local access and specific sequence of tc commands as demonstrated in the vulnerability description.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing commits 38646749d6e12f9d80a08d21ca39f0beca20230d, 46c59ec33ec98aba20c15117630cae43a01404cc, 73c7e1d6898ccbeee126194dcc05f58b8a795e70, 7e2bd8c13b07e29a247c023c7444df23f9a79fd8, bc50835e83f60f56e9bec2b392fb5544f250fb6f
Vendor Advisory: https://git.kernel.org/stable/c/38646749d6e12f9d80a08d21ca39f0beca20230d
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.
🔧 Temporary Workarounds
Restrict CAP_NET_ADMIN capabilities
allLimit which users can execute traffic control commands by removing CAP_NET_ADMIN from non-privileged users
setcap -r /sbin/tc
chmod 750 /sbin/tc
Use sudoers to restrict tc command execution
🧯 If You Can't Patch
- Restrict access to tc command to root only
- Implement strict user privilege separation and remove CAP_NET_ADMIN from regular users
🔍 How to Verify
Check if Vulnerable:
Check kernel version and compare with patched versions from kernel git repositoryCheck Version:
uname -rVerify Fix Applied:
Verify kernel version after update matches patched versions, test tc replace operations no longer allow cross-parent grafting📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- OOPs messages related to net/sched
- Failed tc command executions with specific error patterns
Network Indicators:
- Unusual traffic control configuration changes
- Multiple tc replace operations in short time
SIEM Query:
Process execution: tc with replace parent parameters, Kernel logs containing 'UAF' or 'use-after-free' in net/sched context🔗 References
- https://git.kernel.org/stable/c/38646749d6e12f9d80a08d21ca39f0beca20230d
- https://git.kernel.org/stable/c/46c59ec33ec98aba20c15117630cae43a01404cc
- https://git.kernel.org/stable/c/73c7e1d6898ccbeee126194dcc05f58b8a795e70
- https://git.kernel.org/stable/c/7e2bd8c13b07e29a247c023c7444df23f9a79fd8
- https://git.kernel.org/stable/c/bc50835e83f60f56e9bec2b392fb5544f250fb6f
- https://git.kernel.org/stable/c/cd796e269123e1994bfc4e99dd76680ba0946a97
- https://git.kernel.org/stable/c/deda09c0543a66fa51554abc5ffd723d99b191bf
- https://git.kernel.org/stable/c/fe18c21d67dc7d1bcce1bba56515b1b0306db19b
- https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
- https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
