CVE-2025-39726Network attack vector

Remote service interruption via concurrent ISM command corruption

Published Sep 5, 2025 · Updated Sep 5, 2025

Race condition in the Linux kernel 4.19 through 6.16-rc7 allows remote attackers to disable an s390 ISM function via SMC traffic. ism_cmd() shares one firmware request buffer across CPUs without serializing request-response sequences, so concurrent commands overwrite inputs or outputs. An SMC-enabled listener and s390x ISM hardware are required; connection churn can leave the function in an unrecoverable error state and break current and future connections.

CVSS severity9.8
Critical
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in the Linux kernel 4.19 through 6.16-rc7 allows remote attackers to disable an s390 ISM function via SMC traffic. ism_cmd() shares one firmware request buffer across CPUs without serializing request-response sequences, so concurrent commands overwrite inputs or outputs. An SMC-enabled listener and s390x ISM hardware are required; connection churn can leave the function in an unrecoverable error state and break current and future connections.

The record

CVE
CVE-2025-39726
Published
Sep 5, 2025
Updated
Sep 5, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-362, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 5, 2025Record 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=4.19
  2. Affected versionversion=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <1194ad0d44d66b273a02a3a22882dc863a68d764
  3. Affected versionversion=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <897e8601b9cff1d054cdd53047f568b0e1995726
  4. Affected versionversion=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <faf44487dfc80817f178dc8de7a0b73f960d019b
  5. Affected versionversion=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <fafaa4982bedb5532f5952000f714a3e63023f40

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.19; version=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <1194ad0d44d66b273a02a3a22882dc863a68d764; version=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <897e8601b9cff1d054cdd53047f568b0e1995726; version=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <faf44487dfc80817f178dc8de7a0b73f960d019b; version=684b89bc39ce4f204b1a2b180f39f2eb36a6b695 <fafaa4982bedb5532f5952000f714a3e63023f40

Published CVSS scores

9.8LinuxCVSS:3.1/AV:N/AC:L/PR:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1499Endpoint Denial of Service

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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