CVE-2025-21856

Kernel compromise via premature ISM device free

Published Mar 12, 2025 · Updated May 11, 2026

Use-after-free in the s390 ISM driver in Linux 6.3 and later allows local users to corrupt kernel memory during device removal. The driver calls device_add() and then directly frees its struct device without a release callback, even though sysfs or another kernel subsystem can retain a reference. An affected s390 system must use the ISM driver; dereferencing the stale object can crash the kernel or support privilege escalation.

CVSS severity7.8
High
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the s390 ISM driver in Linux 6.3 and later allows local users to corrupt kernel memory during device removal. The driver calls device_add() and then directly frees its struct device without a release callback, even though sysfs or another kernel subsystem can retain a reference. An affected s390 system must use the ISM driver; dereferencing the stale object can crash the kernel or support privilege escalation.

The record

CVE
CVE-2025-21856
Published
Mar 12, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 12, 2025CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.3
  2. Affected versionversion=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <0505ff2936f166405d81d0d454a81d9c14124344
  3. Affected versionversion=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <915e34d5ad35a6a9e56113f852ade4a730fb88f0
  4. Affected versionversion=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <940d15254d2216b585558bcf36312da50074e711
  5. Affected versionversion=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <e26e8ac27351f457091459a0a355bacd06d5bb2b

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=6.3; version=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <0505ff2936f166405d81d0d454a81d9c14124344; version=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <915e34d5ad35a6a9e56113f852ade4a730fb88f0; version=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <940d15254d2216b585558bcf36312da50074e711; version=8c81ba20349daf9f7e58bb05a0c12f4b71813a30 <e26e8ac27351f457091459a0a355bacd06d5bb2b

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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