CVE-2025-21858
📋 TL;DR
A use-after-free vulnerability in the Linux kernel's GENEVE (Generic Network Virtualization Encapsulation) implementation allows an attacker to cause memory corruption when creating GENEVE network devices across different network namespaces. This affects Linux systems using GENEVE tunneling, potentially leading to kernel crashes or privilege escalation. The vulnerability requires local access or the ability to create network devices.
💻 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
Kernel panic leading to system crash, or potential privilege escalation to root via kernel memory corruption.
Likely Case
Kernel crash or system instability when creating GENEVE devices in specific namespace configurations.
If Mitigated
No impact if GENEVE tunneling is not used or proper namespace isolation is maintained.
🎯 Exploit Status
Requires CAP_NET_ADMIN capability to create network devices and specific namespace manipulation. Discovered via syzkaller fuzzing without public exploit.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with commits: 3ce92ca990cfac88a87c61df3cc0b5880e688ecf, 5a0538ac6826807d6919f6aecbb8996c2865af2c, 788dbca056a8783ec063da3c9d49a3a71c76c283, 904e746b2e7fa952ab8801b303ce826a63153d78, 9593172d93b9f91c362baec4643003dc29802929
Vendor Advisory: https://git.kernel.org/stable/c/3ce92ca990cfac88a87c61df3cc0b5880e688ecf
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel. 3. Verify kernel version matches patched release.
🔧 Temporary Workarounds
Disable GENEVE module
LinuxPrevent loading of GENEVE kernel module if not needed
echo 'install geneve /bin/false' >> /etc/modprobe.d/disable-geneve.conf
rmmod geneve
Restrict CAP_NET_ADMIN
LinuxLimit users/processes with network administration capabilities
Use Linux capabilities system to remove CAP_NET_ADMIN from unnecessary users/containers
🧯 If You Can't Patch
- Avoid using GENEVE tunneling in production environments
- Implement strict namespace isolation and limit cross-namespace device creation
🔍 How to Verify
Check if Vulnerable:
Check if GENEVE module is loaded and kernel version is vulnerable: lsmod | grep geneve && uname -rCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits: uname -r and check with distribution vendor📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- KASAN reports of use-after-free in geneve_find_dev
- System crashes during network device creation
Network Indicators:
- Unusual GENEVE tunnel creation patterns
- Multiple failed network namespace operations
SIEM Query:
Search for kernel logs containing 'geneve_find_dev', 'KASAN: slab-use-after-free', or 'geneve_configure' errors🔗 References
- https://git.kernel.org/stable/c/3ce92ca990cfac88a87c61df3cc0b5880e688ecf
- https://git.kernel.org/stable/c/5a0538ac6826807d6919f6aecbb8996c2865af2c
- https://git.kernel.org/stable/c/788dbca056a8783ec063da3c9d49a3a71c76c283
- https://git.kernel.org/stable/c/904e746b2e7fa952ab8801b303ce826a63153d78
- https://git.kernel.org/stable/c/9593172d93b9f91c362baec4643003dc29802929
- https://git.kernel.org/stable/c/d5e86e27de0936f3cb0a299ce519d993e9cf3886
- https://git.kernel.org/stable/c/da9b0ae47f084014b1e4b3f31f70a0defd047ff3
- https://git.kernel.org/stable/c/f74f6560146714241c6e167b03165ee77a86e316
- https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
- https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
