CVE-2025-39681

Early-boot crash via uninitialized cache scaling value

Published Sep 5, 2025 · Updated Sep 5, 2025

Denial of service in the Linux kernel allows local users to crash Hygon systems with CQM support during early boot. The Hygon BSP initialization omits resctrl_cpu_detect(), leaving boot_cpu_data.x86_cache_occ_scale uninitialized when get_rdt_mon_resources() divides while calculating mon_l3_config. Exposure requires a Hygon x86 CPU advertising X86_FEATURE_CQM*; reaching the fault interrupts startup rather than disclosing or modifying data.

CVSS severity5.5
Medium
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the Linux kernel allows local users to crash Hygon systems with CQM support during early boot. The Hygon BSP initialization omits resctrl_cpu_detect(), leaving boot_cpu_data.x86_cache_occ_scale uninitialized when get_rdt_mon_resources() divides while calculating mon_l3_config. Exposure requires a Hygon x86 CPU advertising X86_FEATURE_CQM*; reaching the fault interrupts startup rather than disclosing or modifying data.

The record

CVE
CVE-2025-39681
Published
Sep 5, 2025
Updated
Sep 5, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
local
Privileges
authenticated

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=5.8
  2. Affected versionversion=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <7207923d8453ebfb35667c1736169f2dd796772e
  3. Affected versionversion=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <873f32201df8876bdb2563e3187e79149427cab4
  4. Affected versionversion=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <a9e5924daa954c9f585c1ca00358afe71d6781c4
  5. Affected versionversion=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <d23264c257a70dbe021b43b3bc2ee16134cd2c69
  6. Affected versionversion=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <d8df126349dad855cdfedd6bbf315bad2e901c2f
  7. Affected versionversion=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <fb81222c1559f89bfe3aa1010f6d112531d55353

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.8; version=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <7207923d8453ebfb35667c1736169f2dd796772e; version=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <873f32201df8876bdb2563e3187e79149427cab4; version=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <a9e5924daa954c9f585c1ca00358afe71d6781c4; version=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <d23264c257a70dbe021b43b3bc2ee16134cd2c69; version=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <d8df126349dad855cdfedd6bbf315bad2e901c2f; version=923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9 <fb81222c1559f89bfe3aa1010f6d112531d55353

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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

No sourced classifications are available.

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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