high CVSS 7.8

CVE-2025-21856·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: s390/ism: add release function for struct device According to device_release() in /drivers/base/core.c, a device without a release function is a broken device and must be fixed. The current code directly frees the device after calling device_add() without waiting for other kernel parts to release their references. Thus, a reference could still be held to a struct device, e.g., by sysfs, leading to potential use-after-free issues if a proper release function is not set.

Severity
high
Software
Kernel
Fixed in
6.13.5
Published
2025-03-12

Affected versions

From: 6.13

Until: 6.13.5

Fixed in: 6.13.5

How to fix this CVE

Update your Linux kernel to version 6.13.5 or later to resolve this device lifecycle management vulnerability in the s390/ism subsystem. The fix implements a proper release function for the struct device, preventing use-after-free conditions that could occur when kernel components maintain references after device removal. Systems running kernel versions 6.13 through 6.13.4 should prioritize this update to eliminate the risk of memory safety violations.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Run 'uname -r' to identify your current kernel version and confirm if it falls within the 6.13.0 to 6.13.4 range
  2. Check if the s390/ism driver is loaded by running 'lsmod | grep ism' on s390x architecture systems
  3. Search kernel logs for use-after-free warnings related to device cleanup: 'sudo dmesg | grep -i "use-after-free\|device.*release\|ism"'
  4. Verify the fix is applied by confirming kernel version is 6.13.5 or higher with 'uname -r'

FAQ

What is CVE-2025-21856?

CVE-2025-21856 is a device lifecycle management vulnerability in the Linux kernel's s390/ism subsystem where the absence of a proper device release function could lead to use-after-free memory conditions when kernel components retain references to freed device structures.

Is CVE-2025-21856 being actively exploited?

No, CVE-2025-21856 is not currently listed on the CISA Known Exploited Vulnerabilities catalog and no public exploits are available.

What versions of Kernel are affected by CVE-2025-21856?

Linux kernel versions 6.13 through 6.13.4 are affected. Kernel version 6.13.5 and later include the fix.

How do I check if my server is vulnerable to CVE-2025-21856?

Run 'uname -r' to check your kernel version. If the output shows version 6.13 through 6.13.4, your system is vulnerable. This vulnerability only affects s390x architecture systems using the ism driver.

Does Defensia detect CVE-2025-21856?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2025-21856 will appear in your dashboard with remediation steps.

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References

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