CVE-2025-39745

Warning splat via incorrect RT softirq-state check

Published Sep 11, 2025 · Updated Sep 11, 2025

Availability flaw in Linux kernel rcutorture allows local users to trigger a kernel warning during tests on PREEMPT_RT builds. rcutorture_one_extend_check() reads preempt_count() to decide whether bottom halves are disabled, but RT kernels do not reflect the relevant softirq bits there. The condition requires CONFIG_PREEMPT_RT=y and an active rcutorture test; the observed consequence is a warning splat rather than disclosed data access or code execution.

CVSS severity5.5
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Availability flaw in Linux kernel rcutorture allows local users to trigger a kernel warning during tests on PREEMPT_RT builds. rcutorture_one_extend_check() reads preempt_count() to decide whether bottom halves are disabled, but RT kernels do not reflect the relevant softirq bits there. The condition requires CONFIG_PREEMPT_RT=y and an active rcutorture test; the observed consequence is a warning splat rather than disclosed data access or code execution.

The record

CVE
CVE-2025-39745
Published
Sep 11, 2025
Updated
Sep 11, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 11, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 11, 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=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <69c5ae0f441c2d72e8f48dc1e08464c172360c4c
  2. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <8d71351d88e478d3c4e945e3218e97ec677fd807
  3. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <a85550267247cdf5e7499be00ea8e388ab014e50

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <69c5ae0f441c2d72e8f48dc1e08464c172360c4c; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <8d71351d88e478d3c4e945e3218e97ec677fd807; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <a85550267247cdf5e7499be00ea8e388ab014e50

Published CVSS scores

5.5UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
2.3Amazon LinuxCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L

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

T1499.004Application or System Exploitation

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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