CVE-2025-21716
📋 TL;DR
A vulnerability in the Linux kernel's VXLAN virtual network filtering function allows reading uninitialized memory when processing malformed netlink messages. This affects systems using VXLAN networking with kernel versions containing the bug. Attackers could potentially leak kernel memory contents.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel memory information disclosure leading to potential privilege escalation or further exploitation through leaked sensitive data like encryption keys or memory addresses.
Likely Case
Information disclosure of kernel memory contents, potentially revealing system state or sensitive data to local attackers.
If Mitigated
Minimal impact with proper kernel hardening and network segmentation limiting access to netlink sockets.
🎯 Exploit Status
Exploitation requires ability to send crafted netlink messages to kernel, typically requiring local access or CAP_NET_ADMIN capabilities. No public exploit code identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in kernel commits: 1693d1fade71646a0731b6b213298cb443d186ea, 5066293b9b7046a906eff60e3949a887ae185a43, a84d511165d6ba7f331b90ae6b6ce180ec534daa, cb1de9309a48cc5b771115781eec05075fd67039, f554bce488605d2f70e06eeab5e4d2448c813713
Vendor Advisory: https://git.kernel.org/stable/c/1693d1fade71646a0731b6b213298cb443d186ea
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Check your distribution's security advisories for specific patched kernel versions. 3. Reboot system after kernel update.
🔧 Temporary Workarounds
Restrict netlink access
linuxLimit which users/processes can send netlink messages to kernel using capabilities or namespaces
# Use Linux capabilities to restrict CAP_NET_ADMIN
# Use network namespaces to isolate VXLAN functionality
# Consider using seccomp filters to block netlink socket calls
🧯 If You Can't Patch
- Implement strict network segmentation to limit access to systems with VXLAN functionality
- Monitor for unusual netlink activity and implement least privilege for processes requiring CAP_NET_ADMIN
🔍 How to Verify
Check if Vulnerable:
Check kernel version and verify if it contains the vulnerable vxlan_vnifilter_dump() function before the fix commitsCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes the fix commits or check with 'uname -r' and compare against patched versions from your distribution📡 Detection & Monitoring
Log Indicators:
- Kernel oops messages related to vxlan_vnifilter_dump
- KMSAN reports of uninit-value access
- Unusual netlink socket activity
Network Indicators:
- Abnormal netlink message patterns to kernel
- Unexpected VXLAN configuration changes
SIEM Query:
source="kernel" AND ("vxlan_vnifilter_dump" OR "KMSAN" OR "uninit-value")🔗 References
- https://git.kernel.org/stable/c/1693d1fade71646a0731b6b213298cb443d186ea
- https://git.kernel.org/stable/c/5066293b9b7046a906eff60e3949a887ae185a43
- https://git.kernel.org/stable/c/a84d511165d6ba7f331b90ae6b6ce180ec534daa
- https://git.kernel.org/stable/c/cb1de9309a48cc5b771115781eec05075fd67039
- https://git.kernel.org/stable/c/f554bce488605d2f70e06eeab5e4d2448c813713
- https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
