CVE-2025-21856
📋 TL;DR
This CVE describes a use-after-free vulnerability in the Linux kernel's s390/ism driver where a struct device is freed without a proper release function. This could allow attackers with local access to potentially crash the system or execute arbitrary code. It affects Linux systems running on IBM s390 architecture with the ISM driver loaded.
💻 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
Local privilege escalation to kernel-level code execution, potentially leading to full system compromise.
Likely Case
Kernel panic or system crash causing denial of service.
If Mitigated
Minimal impact if proper access controls prevent local attackers from triggering the vulnerability.
🎯 Exploit Status
Exploitation requires local access and knowledge of kernel internals. No public exploit code is known at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in stable kernel trees (commits: 0505ff2936f166405d81d0d454a81d9c14124344, 915e34d5ad35a6a9e56113f852ade4a730fb88f0, 940d15254d2216b585558bcf36312da50074e711, e26e8ac27351f457091459a0a355bacd06d5bb2b)
Vendor Advisory: https://git.kernel.org/stable/c/0505ff2936f166405d81d0d454a81d9c14124344
Restart Required: Yes
Instructions:
1. Update to a patched kernel version from your distribution vendor. 2. Reboot the system to load the new kernel. 3. Verify the patch is applied by checking kernel version or commit hash.
🔧 Temporary Workarounds
Unload ISM driver
Linux s390Remove the vulnerable driver module if not required for system operation
modprobe -r ism
🧯 If You Can't Patch
- Restrict local user access to systems running vulnerable kernels
- Implement strict privilege separation and limit user capabilities
🔍 How to Verify
Check if Vulnerable:
Check if ISM driver is loaded: lsmod | grep ism AND check kernel version against patched versionsCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes the fix commits or check that ISM driver is not loaded if using workaround📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- Oops messages related to ISM driver or device release
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
Search for kernel panic events or system crashes on s390 systems with ISM driver