CVE-2025-39851
📋 TL;DR
A NULL pointer dereference vulnerability in the Linux kernel's VXLAN implementation allows local attackers to cause a kernel panic (denial of service) by sending specially crafted packets. This affects Linux systems using VXLAN with learning enabled and FDB nexthop groups configured. The vulnerability requires local network access to exploit.
💻 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
Kernel panic leading to system crash and denial of service, potentially disrupting network connectivity and services.
Likely Case
Local denial of service affecting VXLAN functionality, causing network disruption for affected interfaces.
If Mitigated
Minimal impact if proper network segmentation and access controls prevent unauthorized local network access.
🎯 Exploit Status
Proof-of-concept script provided in CVE description requires local network access and specific VXLAN configuration.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with fixes from the referenced commits
Vendor Advisory: https://git.kernel.org/stable/c/0e8630f24c14d9c655d19eabe2e52a9e9f713307
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing fixes 2. Reboot system 3. Verify kernel version after reboot
🔧 Temporary Workarounds
Disable VXLAN learning
LinuxPrevent the vulnerable code path by disabling learning on VXLAN interfaces
ip link set dev <vxlan_interface> type vxlan learning off
Network segmentation
allRestrict access to VXLAN interfaces to trusted hosts only
🧯 If You Can't Patch
- Implement strict network access controls to prevent unauthorized access to VXLAN interfaces
- Monitor for kernel panic events and unusual VXLAN traffic patterns
🔍 How to Verify
Check if Vulnerable:
Check if system uses VXLAN with learning enabled and FDB nexthop groups, and kernel version is before fixesCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes fixes from referenced commits and test with reproduction script📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs mentioning NULL pointer dereference in vxlan_snoop
- System crash/reboot events
Network Indicators:
- Unusual VXLAN packet patterns targeting MAC addresses with nexthop groups
SIEM Query:
event_type:kernel_panic AND message:"NULL pointer dereference" AND message:"vxlan"