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CVE-2025-21865 Siemens CVE debrief

CVE-2025-21865 is a local-attack, availability-impact vulnerability tied by Siemens and CISA to select SIMATIC S7-1500 CPU models that include a GNU/Linux subsystem. The underlying issue described in the CVE record is a kernel teardown bug in gtp_net_exit_batch_rtnl() where device deletion can be triggered twice during exit_batch_rtnl(), creating a list-corruption condition. Siemens’ advisory and the CISA CSAF record rate the issue as high-availability impact, and the published remediation states that no fix is currently available.

Vendor
Siemens
Product
SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2025-06-10
Original CVE updated
2026-05-14
Advisory published
2025-06-10
Advisory updated
2026-05-14

Who should care

OT operators, plant engineers, and asset owners running the affected SIMATIC S7-1500 CPU variants should pay attention, especially if the device’s GNU/Linux subsystem is enabled or accessible. Security teams responsible for local account control, application provenance, and maintenance windows should also review this advisory.

Technical summary

The public CVE description identifies a bug in the gtp network tunnel exit path: a loop added in gtp_net_exit_batch_rtnl() can cause ->dellink() to be called twice for the same device during ->exit_batch_rtnl(). Siemens’ CSAF advisory maps this to affected SIMATIC S7-1500 CPU products and describes a mitigation posture focused on restricting interactive shell access to trusted personnel and only running trusted applications. The advisory’s CVSS vector is AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, indicating local access is required and the primary impact is denial of service/availability loss.

Defensive priority

Medium. Prioritize if the affected CPU family is deployed in operationally critical environments, if local shell access is broader than necessary, or if third-party applications are executed on the GNU/Linux subsystem. Because the advisory states that no fix is currently available, compensating controls matter more than patching in the short term.

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.
  • Inventory affected SIMATIC S7-1500 CPU models and confirm whether the GNU/Linux subsystem is enabled in your deployment.
  • Track Siemens ProductCERT SSA-082556 and CISA ICSA-25-162-05 for any future remediation updates.
  • Apply least-privilege controls for local users and maintenance accounts that can interact with the subsystem.

Evidence notes

CISA’s CSAF record for ICSA-25-162-05 was published on 2025-06-10 and last updated on 2026-05-14. The advisory lists five affected Siemens CPU product identifiers and explicitly states that no fix is currently available. The remediation entries provided are limited to trusted-shell access and trusted application sources. The CVE text describes a duplicate device deletion path in gtp_net_exit_batch_rtnl(), and the official CVSS vector is AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21865 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21865

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

  • CVE-2025-21865 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21865

    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/2025/icsa-25-162-05.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-082556.json

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-082556.html

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-25-162-05

    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.