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CVE-2025-21726 Siemens CVE debrief

CVE-2025-21726 is a Use-After-Free (UAF) vulnerability in the Linux kernel's padata subsystem, specifically affecting the `reorder_work` function. The vulnerability was published on 2024-04-09 and last modified on 2026-05-14. Siemens has identified this vulnerability as affecting the GNU/Linux subsystem of the SIMATIC S7-1500 TM MFP industrial control system. The vulnerability carries a CVSS 3.1 score of 7.8 (HIGH severity) with a vector of AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, indicating that a local attacker with low privileges can achieve high impact on confidentiality, integrity, and availability without user interaction. The padata subsystem is used for parallel data processing in the kernel, and the UAF condition in `reorder_work` could potentially allow privilege escalation or system compromise. As of the advisory publication, no patch is available from Siemens for this specific product. The vulnerability was added to the CISA ICS advisory ICSA-24-102-01 in Additional Release 8 on 2025-08-12, along with 147 other CVEs.

Vendor
Siemens
Product
SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2024-04-09
Original CVE updated
2026-05-14
Advisory published
2024-04-09
Advisory updated
2026-05-14

Who should care

Organizations operating Siemens SIMATIC S7-1500 TM MFP systems with the GNU/Linux subsystem enabled, particularly in industrial automation and manufacturing environments. Security teams responsible for OT/ICS infrastructure should prioritize access controls given the absence of available patches.

Technical summary

The vulnerability exists in the Linux kernel's padata (parallel data) subsystem, which provides infrastructure for parallelizing CPU-intensive operations. The `reorder_work` function contains a use-after-free condition that can be triggered during reordering operations. On affected Siemens SIMATIC S7-1500 TM MFP systems, the GNU/Linux subsystem exposes this kernel-level vulnerability to potential local exploitation. The CVSS vector indicates local attack vector with low attack complexity, requiring low privileges but granting high impact across all three security dimensions (CIA triad).

Defensive priority

HIGH

Recommended defensive actions

  • Restrict interactive shell access to the GNU/Linux subsystem to trusted personnel only
  • Only build and run applications from trusted sources
  • Monitor for future Siemens security advisories (SSA-265688) for patch availability
  • Apply defense-in-depth strategies for industrial control systems per CISA guidance
  • Review and implement ICS-CERT recommended practices for securing control system environments

Evidence notes

Vulnerability description sourced from CISA CSAF advisory ICSA-24-102-01. CVSS vector and score confirmed from source metadata. Affected product identified as SIMATIC S7-1500 TM MFP GNU/Linux subsystem via CSAF product tree. Timeline of advisory updates tracked through revision history showing CVE added in Additional Release 8 (2025-08-12).

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21726 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21726

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

  • CVE-2025-21726 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21726

    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.