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PatchSiren cyber security CVE debrief

CVE-2025-21719 Siemens CVE debrief

CVE-2025-21719 is a vulnerability in the Linux kernel's IP multicast routing (ipmr) subsystem. The issue occurs when the kernel incorrectly calls `mr_mfc_uses_dev()` on unresolved multicast forwarding cache (MFC) entries, which can lead to a denial of service condition. The vulnerability has a CVSS 3.1 score of 5.5 (MEDIUM severity) with a local attack vector requiring low privileges. Siemens has identified this vulnerability as affecting the GNU/Linux subsystem of the SIMATIC S7-1500 TM MFP industrial control system. The vulnerability was first published on April 9, 2024, and the advisory has been updated multiple times through September 2025 to include additional related CVEs. No patch is currently available from Siemens for this product.

Vendor
Siemens
Product
SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
CVSS
HIGH 7.1
CISA KEV
Not listed in stored evidence
Original CVE published
2025-02-27
Original CVE updated
2026-07-30
Advisory published
2025-02-27
Advisory updated
2026-07-30

Who should care

Organizations operating Siemens SIMATIC S7-1500 TM MFP systems in industrial environments, particularly those utilizing the GNU/Linux subsystem for custom applications. System administrators responsible for OT/ICS security and personnel managing multicast networking configurations should prioritize access controls given the absence of an available patch. CISOs and OT security teams should incorporate this into risk assessments for defense-in-depth strategies.

Technical summary

The vulnerability exists in the Linux kernel's IP multicast routing (ipmr) implementation. The function `mr_mfc_uses_dev()` is incorrectly invoked on unresolved MFC (multicast forwarding cache) entries, which can trigger a denial of service condition. This is a local vulnerability requiring low privileges with no user interaction needed. The attack impacts availability only (no confidentiality or integrity impact per CVSS). The affected product is the GNU/Linux subsystem within Siemens' SIMATIC S7-1500 TM MFP, an industrial technology CPU with multifunctional platform capabilities.

Defensive priority

medium

Recommended defensive actions

  • Limit access to the interactive shell of the additional GNU/Linux subsystem to trusted personnel only
  • Only build and run applications from trusted sources
  • Monitor for future security updates from Siemens for the SIMATIC S7-1500 TM MFP product line
  • Apply defense-in-depth strategies for industrial control systems per CISA guidance

Evidence notes

The vulnerability description 'ipmr: do not call mr_mfc_uses_dev() for unres entries' indicates a kernel-level issue in the IP multicast routing implementation. The CVSS vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) confirms local attack requirements with high availability impact. Siemens remediation guidance explicitly states 'Currently no fix is available' as of the advisory publication.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21719 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21719

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

  • CVE-2025-21719 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21719

    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.