CVE-2025-21703
📋 TL;DR
This is a use-after-free vulnerability in the Linux kernel's netem network emulation subsystem. It allows attackers with local access to potentially cause kernel crashes or execute arbitrary code. Systems running vulnerable Linux kernel versions with netem enabled 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 →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 system crash, or arbitrary code execution in kernel context.
Likely Case
Kernel panic leading to denial of service (system crash) or system instability.
If Mitigated
Limited to denial of service if exploit fails or system has additional kernel hardening protections.
🎯 Exploit Status
Requires local access and knowledge of kernel exploitation techniques. Use-after-free vulnerabilities can be challenging to exploit reliably.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing commits: 1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5, 6312555249082d6d8cc5321ff725df05482d8b83, 638ba5089324796c2ee49af10427459c2de35f71, 7b79ca9a1de6a428d486ff52fb3d602321c08f55, 7f31d74fcc556a9166b1bb20515542de7bb939d1
Vendor Advisory: https://git.kernel.org/stable/c/1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution vendor. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.
🔧 Temporary Workarounds
Disable netem qdisc
LinuxRemove or disable netem network emulation if not required
tc qdisc del dev <interface> root netem
Check with: tc qdisc show
🧯 If You Can't Patch
- Restrict local user access to systems where netem is enabled
- Implement kernel hardening features like KASLR, stack protection, and SMAP/SMEP
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if netem is configured: uname -r && tc qdisc show | grep netemCheck Version:
uname -rVerify Fix Applied:
Verify kernel version is updated and no longer vulnerable: uname -r📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages in /var/log/kern.log or dmesg
- OOM killer activity related to kernel memory
Network Indicators:
- Unusual netem configuration changes
SIEM Query:
source="kernel" AND ("panic" OR "Oops" OR "general protection fault")🔗 References
- https://git.kernel.org/stable/c/1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5
- https://git.kernel.org/stable/c/6312555249082d6d8cc5321ff725df05482d8b83
- https://git.kernel.org/stable/c/638ba5089324796c2ee49af10427459c2de35f71
- https://git.kernel.org/stable/c/7b79ca9a1de6a428d486ff52fb3d602321c08f55
- https://git.kernel.org/stable/c/7f31d74fcc556a9166b1bb20515542de7bb939d1
- https://git.kernel.org/stable/c/839ecc583fa00fab785fde1c85a326743657fd32
- https://git.kernel.org/stable/c/98a2c685293aae122f688cde11d9334dddc5d207
- https://git.kernel.org/stable/c/e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c
- https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
