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PatchSiren cyber security CVE debrief

CVE-2025-21760 Siemens CVE debrief

CVE-2025-21760 is a HIGH severity vulnerability (CVSS 7.8) affecting the Linux kernel's IPv6 Neighbor Discovery (NDISC) subsystem. The issue involves insufficient RCU (Read-Copy-Update) protection in the ndisc_send_skb() function, which can lead to use-after-free conditions. 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 their SIMATIC S7-1500 TM MFP industrial control system product. The vulnerability requires local access with low privileges, but successful exploitation can result in high impact to confidentiality, integrity, and availability. No patch is currently available from Siemens for the affected product.

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
2026-07-14
Original CVE updated
2026-07-28
Advisory published
2026-07-14
Advisory updated
2026-07-28

Who should care

Organizations operating Siemens SIMATIC S7-1500 TM MFP industrial control systems with the GNU/Linux subsystem enabled should prioritize this vulnerability. System administrators, OT security teams, and industrial asset owners in manufacturing, process control, and critical infrastructure sectors need to assess their exposure and implement compensating controls until a vendor patch becomes available.

Technical summary

This vulnerability exists in the Linux kernel's IPv6 Neighbor Discovery protocol implementation. The ndisc_send_skb() function lacks proper RCU protection, creating a race condition that can result in use-after-free memory corruption. The vulnerability is classified under CWE-416 (Use After Free). In the context of Siemens SIMATIC S7-1500 TM MFP, the GNU/Linux subsystem is affected, potentially allowing an attacker with local access to escalate privileges or cause denial of service. The attack requires local access but no user interaction, with successful exploitation yielding complete compromise of the affected system's confidentiality, integrity, and availability.

Defensive priority

HIGH

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 vendor security advisories from Siemens for future patch availability
  • Apply network segmentation to limit exposure of affected industrial control systems
  • Review and implement CISA ICS recommended practices for defense in depth

Evidence notes

The vulnerability description indicates this is a kernel-level RCU protection issue in the IPv6 neighbor discovery implementation. The CVSS vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) confirms local attack vector with low complexity and high impact potential. The source advisory (ICSA-24-102-01) from CISA's CSAF repository provides official vendor acknowledgment through Siemens.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21760 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21760

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

  • CVE-2025-21760 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21760

    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.