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PatchSiren cyber security CVE debrief

CVE-2025-39701 Siemens CVE debrief

CVE-2025-39701 is a firmware-update validation issue described in a CISA-republished Siemens advisory. The advisory text says the driver should use the security-version-number check instead of the runtime version check, because the old logic could cause a firmware update to fail when the update binary has a lower runtime version number than the installed one. Source materials associate the issue with Siemens SIMATIC CN 4100 versions earlier than V5.0, and the provided remediation is to update to V5.0 or later.

Vendor
Siemens
Product
SIMATIC CN 4100
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-12
Original CVE updated
2026-05-14
Advisory published
2026-05-12
Advisory updated
2026-05-14

Who should care

Operators and maintainers responsible for Siemens SIMATIC CN 4100 deployments, especially environments that rely on firmware update workflows. Security teams should also care because the source advisory ties the issue to an industrial-control/OT product and the CVSS vector indicates local, low-privilege conditions with high availability impact.

Technical summary

The source advisory describes a logic error in the ACPI pfr_update driver update path: the code checks runtime version rather than security-version-number semantics. That mismatch can block legitimate firmware updates when the package's runtime version is lower even though the security version is appropriate. The supplied CVSS vector is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, which aligns with a local issue that primarily affects availability rather than confidentiality or integrity.

Defensive priority

Medium. The issue is not marked as KEV and the provided vector indicates local access is required, but it can interfere with firmware maintenance and availability. Treat it as a patch-planning item for affected Siemens deployments and verify whether the advisory's product scope applies to your environment.

Recommended defensive actions

  • Confirm whether Siemens SIMATIC CN 4100 systems in your environment are affected by the advisory scope 'vers:intdot/<5.0'.
  • Apply the vendor remediation and update to V5.0 or later as cited in the advisory.
  • Review firmware update validation procedures to ensure security-version-number checks are used where applicable.
  • Retest update workflows after patching to confirm legitimate firmware packages are accepted.
  • Track the CISA/Siemens advisory for any follow-up clarifications or revised applicability guidance.

Evidence notes

CISA's republished advisory states: 'The security-version-number check should be used rather than the runtime version check for driver updates.' It also lists the affected product as 'Siemens SIMATIC CN 4100 vers:intdot/<5.0' and the remediation as 'Update to V5.0 or later version.' The supplied CVSS vector is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, indicating local access requirements and a high availability impact. The vendor/product mapping in the source is low-confidence in the provided enrichment and should be reviewed before broad application.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-39701 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-39701

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2025-39701 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-39701

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source item URL

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/OT/white/2026/icsa-26-134-10.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-032379.json

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-032379.html

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-26-134-10

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-alerts/ics-alert-10-301-01

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/resources-tools/resources/ics-recommended-practices

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/topics/industrial-control-systems

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/recommended_practices/NCCIC_ICS-CERT_Defense_in_Depth_2016_S508C.pdf

    Reference

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.