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CVE-2025-21724 Siemens CVE debrief

CVE-2025-21724 is a local memory-safety issue in the Linux iommufd/iova_bitmap code path that Siemens included in its SIMATIC S7-1500 CPU family advisory. The problem is a shift-out-of-bounds in iova_bitmap_offset_to_index(): the expression shifts the integer literal 1 by bitmap->mapped.pgshift, and when pgshift is greater than 31 on a typical 32-bit int, the shift becomes undefined behavior. CISA’s CSAF for Siemens lists five affected SIMATIC/SIPLUS CPU models and states that no fix is currently available. Siemens recommends restricting shell access to trusted personnel and only building/running applications from trusted sources.

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 security teams, plant operators, and administrators responsible for the listed Siemens SIMATIC S7-1500 CPU 1518/1518F MFP variants, especially environments that expose or use the additional GNU/Linux subsystem or interactive shell.

Technical summary

The advisory describes a UBSAN-detected shift-out-of-bounds in iova_bitmap_offset_to_index(). The buggy operation shifts the constant 1, which defaults to a signed int, by bitmap->mapped.pgshift. If pgshift exceeds the bit width of that type (for example, 63), the result cannot be represented and the shift has undefined behavior. The CSAF lists the issue as affecting five Siemens products and classifies it with CVSS 3.1 vector AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, indicating local attack conditions and high availability impact.

Defensive priority

Medium. The issue is locally exploitable according to the published CVSS vector, affects specific OT CPU products, and currently has no vendor fix in the supplied advisory.

Recommended defensive actions

  • Verify whether any of the five listed Siemens SIMATIC/SIPLUS CPU models are deployed in your environment.
  • Restrict access to the additional GNU/Linux subsystem shell to trusted personnel only, as recommended in the advisory.
  • Only build and run applications from trusted sources on affected systems.
  • Monitor Siemens ProductCERT and CISA for an updated advisory or remediation release.
  • Apply a fix or compensating control promptly when Siemens publishes one.
  • Inventory OT assets that use the affected CPU family and document exposure to local shell or application execution paths.

Evidence notes

The supplied CISA CSAF advisory (ICSA-25-162-05) for Siemens SIMATIC S7-1500 CPU family lists CVE-2025-21724, the five affected product IDs/names, and the remediation note that no fix is currently available. Siemens’ referenced SSA-082556 advisory is the vendor source linked from the CSAF. The CVSS vector in the corpus is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. Timing context is based on the CVE/source publication date of 2025-06-10 and the latest supplied modification date of 2026-05-14.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21724 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21724

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

  • CVE-2025-21724 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-21724

    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.