CVE-2025-21714
📋 TL;DR
A use-after-free vulnerability in the Linux kernel's RDMA/mlx5 driver allows double queueing of implicit ODP MR destroy work, potentially leading to memory corruption. This affects systems using RDMA with mlx5 hardware and can cause kernel crashes or instability. The vulnerability requires local access to exploit.
💻 Affected Systems
- Linux kernel with mlx5 RDMA driver
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to system crash, denial of service, or potential privilege escalation if combined with other vulnerabilities.
Likely Case
System instability, kernel crashes, or denial of service affecting RDMA functionality.
If Mitigated
Minimal impact with proper access controls preventing local exploitation.
🎯 Exploit Status
Exploitation requires local access and knowledge of RDMA operations to trigger the double queueing condition.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel with commit 7cc8f681f6d4ae4478ae0f60485fc768f2b450da or later
Vendor Advisory: https://git.kernel.org/stable/c/7cc8f681f6d4ae4478ae0f60485fc768f2b450da
Restart Required: No
Instructions:
1. Update Linux kernel to version containing the fix commit. 2. For distributions: Use package manager to update kernel package. 3. Rebuild kernel if using custom kernel. 4. No reboot required for live patching systems, otherwise reboot to load new kernel.
🔧 Temporary Workarounds
Disable RDMA mlx5 driver
LinuxPrevent loading of vulnerable mlx5 RDMA driver module
echo 'blacklist mlx5_ib' >> /etc/modprobe.d/blacklist.conf
rmmod mlx5_ib
Restrict RDMA access
LinuxLimit which users/processes can access RDMA devices
chmod 600 /dev/infiniband/*
setfacl -m u:root:rw /dev/infiniband/*
🧯 If You Can't Patch
- Implement strict access controls to limit which users can use RDMA functionality
- Monitor system logs for refcount warnings or kernel panics related to mlx5_ib
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if mlx5_ib module is loaded: uname -r && lsmod | grep mlx5_ibCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commit: git log --oneline | grep '7cc8f681f6d4'📡 Detection & Monitoring
Log Indicators:
- Kernel logs showing 'refcount_t: underflow; use-after-free'
- Warnings from free_implicit_child_mr_work
- Kernel panic messages
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND ("refcount_warn_saturate" OR "free_implicit_child_mr_work" OR "use-after-free")