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CVE-2025-21848 Siemens CVE debrief

CVE-2025-21848 is a null pointer dereference issue in the Linux kernel nfp BPF path, where nfp_bpf_cmsg_alloc() should check the return value of nfp_app_ctrl_msg_alloc(). Siemens’ advisory maps this issue to several SIMATIC S7-1500 CPU family products and states that no fix is currently available. The practical concern in the supplied advisory is availability impact rather than confidentiality or integrity loss.

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

Siemens SIMATIC S7-1500 operators and integrators, especially anyone running the listed CPU models in production or using the additional GNU/Linux subsystem and its shell access.

Technical summary

The supplied description says the kernel fix adds a missing return-value check for nfp_app_ctrl_msg_alloc() inside nfp_bpf_cmsg_alloc() to prevent a null pointer dereference. The CISA-republished Siemens CSAF advisory (ICSA-25-162-05 / SSA-082556) lists five affected SIMATIC S7-1500 CPU product variants and gives CVSS v3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, indicating a local, low-privilege condition with high availability impact. The advisory also states that no fix is currently available.

Defensive priority

Medium overall, but treat as time-sensitive for affected production CPUs because the advisory lists no fix and only mitigation guidance.

Recommended defensive actions

  • Identify whether any of the five listed Siemens SIMATIC S7-1500 CPU variants are deployed in your environment.
  • Restrict access to the interactive shell of the additional GNU/Linux subsystem to trusted personnel only.
  • Only build and run applications from trusted sources on affected systems.
  • Apply Siemens and CISA defense-in-depth guidance and segment affected industrial control assets where possible.
  • Monitor Siemens ProductCERT and CISA advisory updates for a future fix or revised mitigation guidance.

Evidence notes

Grounded in the supplied CISA CSAF source ICSA-25-162-05 (SSA-082556), initially published 2025-06-10 and last updated 2026-05-14. The advisory lists five affected Siemens products, states 'Currently no fix is available,' and includes mitigations limiting shell access and trusting application sources. The description explicitly ties the issue to a missing return-value check for nfp_app_ctrl_msg_alloc() in nfp_bpf_cmsg_alloc() to prevent a null pointer dereference. The provided CVSS vector is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. No KEV listing is indicated in the supplied enrichment.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21848 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21848

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

  • CVE-2025-21848 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21848

    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.