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CVE-2025-21846 Siemens CVE debrief

CVE-2025-21846 is a MEDIUM severity vulnerability (CVSS 5.5) affecting the GNU/Linux subsystem of Siemens SIMATIC S7-1500 TM MFP industrial control devices. The vulnerability involves the Linux kernel's process accounting (acct) subsystem, where the last write operation is performed from a workqueue context. This local attack vector vulnerability requires low privileges and no user interaction, with availability impact rated as HIGH. The vulnerability was first published on April 9, 2024, and has been tracked through multiple advisory updates through September 2025. No patch is currently available from the vendor.

Vendor
Siemens
Product
SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-14
Original CVE updated
2026-07-28
Advisory published
2026-07-14
Advisory updated
2026-07-28

Who should care

Industrial control system operators, OT security teams, and asset owners using Siemens SIMATIC S7-1500 TM MFP devices with the GNU/Linux subsystem enabled should prioritize this vulnerability. Organizations in manufacturing, process control, and critical infrastructure sectors relying on these programmable logic controllers for automation should assess exposure and implement compensating controls until a patch becomes available.

Technical summary

The vulnerability exists in the Linux kernel's process accounting (acct) implementation within the GNU/Linux subsystem of Siemens SIMATIC S7-1500 TM MFP devices. The flaw relates to performing the last write operation from a workqueue context, which can lead to availability impacts. The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) indicates a local attack vector with low attack complexity, requiring low privileges but no user interaction, resulting in high availability impact with no confidentiality or integrity impact.

Defensive priority

medium

Recommended defensive actions

  • Restrict interactive shell access to the GNU/Linux subsystem to trusted personnel only
  • Implement application whitelisting - only build and run applications from trusted sources
  • Monitor for anomalous process accounting activity on affected devices
  • Apply defense-in-depth strategies per ICS-CERT recommended practices
  • Subscribe to Siemens ProductCERT security advisories for patch availability updates

Evidence notes

Evidence derived from CISA ICS advisory ICSA-24-102-01 and Siemens security advisory SSA-265688. CVSS vector confirms local attack vector with low attack complexity.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21846 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21846

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

  • CVE-2025-21846 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21846

    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/2024/icsa-24-102-01.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-265688.json

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-265688.html

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-24-102-01

    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.