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PatchSiren cyber security CVE debrief

CVE-2025-21859 Siemens CVE debrief

CVE-2025-21859 is a medium-severity vulnerability (CVSS 5.5) affecting the USB gadget MIDI function driver (f_midi) in the Linux kernel. The issue involves the f_midi_complete function failing to properly call queue_work, which can lead to a denial-of-service condition. This vulnerability impacts Siemens SIMATIC S7-1500 TM MFP industrial control systems through their GNU/Linux subsystem. The vulnerability was 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 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
2024-04-09
Original CVE updated
2026-05-14
Advisory published
2024-04-09
Advisory updated
2026-05-14

Who should care

Industrial control system operators, OT security teams, and organizations using Siemens SIMATIC S7-1500 TM MFP systems in manufacturing, process control, or critical infrastructure environments should prioritize access controls and monitoring for this vulnerability given the lack of available patches.

Technical summary

The vulnerability exists in the Linux kernel's USB gadget MIDI function driver (f_midi). The f_midi_complete function does not properly invoke queue_work, which can result in work items not being scheduled correctly. This local vulnerability requires low privileges to exploit and can cause high availability impact (denial of service) on affected systems. The vulnerability affects the GNU/Linux subsystem of Siemens SIMATIC S7-1500 TM MFP programmable logic controllers used in industrial automation environments.

Defensive priority

medium

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 vendor security updates from Siemens
  • Apply defense-in-depth strategies for industrial control systems per CISA guidance
  • Segment affected systems from untrusted networks where possible

Evidence notes

Vulnerability description sourced from CISA CSAF advisory ICSA-24-102-01. Affected product confirmed as Siemens SIMATIC S7-1500 TM MFP GNU/Linux subsystem. CVSS vector AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H indicates local attack vector with low attack complexity, requiring low privileges, resulting in high availability impact. Advisory revision history shows ongoing updates through September 2025.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21859 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21859

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

  • CVE-2025-21859 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21859

    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.