CVE-2025-39742

Kernel crash via unchecked core-sibling divisor

Published Sep 11, 2025 · Updated May 12, 2026

Divide-by-zero in Linux kernel hfi1 CPU-affinity code allows local users to crash affected systems via RDMA affinity calculation. The find_hw_thread_mask() function divides the online-CPU count by affinity->num_core_siblings before checking whether that divisor is zero. Reachability requires hfi1 driver execution and a zero num_core_siblings topology value; the documented consequence is an availability-only kernel crash.

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

Divide-by-zero in Linux kernel hfi1 CPU-affinity code allows local users to crash affected systems via RDMA affinity calculation. The find_hw_thread_mask() function divides the online-CPU count by affinity->num_core_siblings before checking whether that divisor is zero. Reachability requires hfi1 driver execution and a zero num_core_siblings topology value; the documented consequence is an availability-only kernel crash.

The record

CVE
CVE-2025-39742
Published
Sep 11, 2025
Updated
May 12, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-369, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 11, 2025CVE publishedPublication date reported by the CVE source.
  2. May 12, 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=4.8
  2. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <1a7cf828ed861de5be1aff99e10f114b363c19d3
  3. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <31d0599a23efdbfe579bfbd1eb8f8c942f13744d
  4. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <4b4317b0d758ff92ba96f4e448a8992a6fe607bf
  5. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <59f7d2138591ef8f0e4e4ab5f1ab674e8181ad3a
  6. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <89fdac333a17ed990b41565630ef4791782e02f5
  7. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <9b05e91afe948ed819bf87d7ba0fccf451ed79a6
  8. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <9bba1a9994c523b44db64f63b564b4719ea2b7ef
  9. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <9d3211cb61a0773a2440d0a0698c1e6e7429f907
  10. Affected versionversion=b094a36f90975373c3a241839869217a65f17d81 <ac53f377393cc85156afdc90b636e84e544a6f96

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.8; version=b094a36f90975373c3a241839869217a65f17d81 <1a7cf828ed861de5be1aff99e10f114b363c19d3; version=b094a36f90975373c3a241839869217a65f17d81 <31d0599a23efdbfe579bfbd1eb8f8c942f13744d; version=b094a36f90975373c3a241839869217a65f17d81 <4b4317b0d758ff92ba96f4e448a8992a6fe607bf; version=b094a36f90975373c3a241839869217a65f17d81 <59f7d2138591ef8f0e4e4ab5f1ab674e8181ad3a; version=b094a36f90975373c3a241839869217a65f17d81 <89fdac333a17ed990b41565630ef4791782e02f5; version=b094a36f90975373c3a241839869217a65f17d81 <9b05e91afe948ed819bf87d7ba0fccf451ed79a6; version=b094a36f90975373c3a241839869217a65f17d81 <9bba1a9994c523b44db64f63b564b4719ea2b7ef; version=b094a36f90975373c3a241839869217a65f17d81 <9d3211cb61a0773a2440d0a0698c1e6e7429f907; version=b094a36f90975373c3a241839869217a65f17d81 <ac53f377393cc85156afdc90b636e84e544a6f96
Siemens · SIMATIC CN 4100version=0 <V5.0

Published CVSS scores

5.5Siemens ProductCERTCVSS: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

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-369Divide By Zero
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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