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PatchSiren cyber security CVE debrief

CVE-2025-39857 Siemens CVE debrief

CVE-2025-39857 is a Linux kernel NULL pointer dereference in the SMC/RDMA path, documented by CISA and Siemens ProductCERT. The advisory says the issue can be triggered when a software RoCE device is used and the kernel reaches smc_ib_is_sg_need_sync() with ibdev->dma_device set to null, which can crash the system; Siemens recommends updating SIMATIC CN 4100 to V5.0 or later.

Vendor
Siemens
Product
SIMATIC CN 4100
CVSS
HIGH 7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-12
Original CVE updated
2026-05-14
Advisory published
2026-05-12
Advisory updated
2026-05-14

Who should care

Operators and maintainers of Siemens SIMATIC CN 4100 systems running versions before V5.0, especially where Linux SMC/RDMA and software RoCE are in use. Security teams responsible for industrial Linux hosts should also treat this as a high-priority stability and hardening fix.

Technical summary

The advisory describes a NULL pointer dereference in smc_ib_is_sg_need_sync() inside the Linux kernel SMC stack. The failure appears in the smc_listen_work path during buffer/device setup, and the supplied notes state that when a software RoCE device is used, ibdev->dma_device can be null. The fix adds null-pointer detection before the code uses that field.

Defensive priority

High. The advisory assigns CVSS 7.0 (HIGH) and the failure is in kernel code on an industrial product path. Even if the most visible symptom is a crash/oops, kernel faults in operational systems can create meaningful availability risk.

Recommended defensive actions

  • Apply Siemens guidance: update SIMATIC CN 4100 to V5.0 or later.
  • Review whether software RoCE is enabled or otherwise reachable on affected systems.
  • Prioritize patching or maintenance windows for affected industrial Linux deployments before broadening exposure.
  • Monitor affected hosts for kernel oopses or repeated workqueue crashes involving smc_listen_work or smc_ib_is_sg_need_sync().
  • Verify vendor advisory applicability against the exact deployed product and version, since the supplied source marks the product mapping as low confidence and needs review.

Evidence notes

Source material is limited to the supplied CISA CSAF advisory and its linked Siemens ProductCERT references. The supplied timeline shows initial publication on 2026-05-12 and a CISA republication on 2026-05-14; these dates are used only as advisory timing, not as vulnerability creation dates. The advisory text explicitly states that software RoCE can leave ibdev->dma_device null and that null detection was added to prevent the fault. Vendor/product metadata in the prompt is marked low confidence and needs review, so applicability should be validated against the exact environment.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-39857 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-39857

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

  • CVE-2025-39857 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-39857

    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/2026/icsa-26-134-10.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-032379.json

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-032379.html

    Reference

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-26-134-10

    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.