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CVE-2025-38685 Siemens CVE debrief

CVE-2025-38685 is a high-severity memory corruption issue in the Linux kernel fbdev console/framebuffer mapping path. The advisory says a userspace ioctl (FBIOPUT_CON2FBMAP) can map a console to a framebuffer, but if the required console resize fails and execution continues, later screen-update logic can mix stale vc_data references with the newly mapped framebuffer state. That unsafe state can lead to an out-of-bounds write in fast_imageblit(), with the source specifically noting invalid struct references in fbcon_putcs() when the affected console is visible.

Vendor
Siemens
Product
SIMATIC CN 4100
CVSS
HIGH 7.8
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

System owners and operators responsible for the affected Siemens SIMATIC CN 4100 systems listed in the advisory, plus administrators of Linux deployments that use the fbdev/framebuffer console path. Local users with access on the affected system are relevant because the CVSS vector requires local access.

Technical summary

The vulnerable flow is in fbdev console-to-framebuffer remapping. When FBIOPUT_CON2FBMAP is used, the code attempts to resize the console to match framebuffer parameters. If vc_do_resize() fails, the code path described in the advisory continues anyway, leaving a mismatch between vc_data from the previous framebuffer and display variables pointing to the new framebuffer. That state can reach fast_imageblit() and cause an out-of-bounds write. The supplied CVSS vector is AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, and the advisory cites CWE-787.

Defensive priority

High. The issue is locally reachable, rated CVSS 7.8, and can produce memory corruption with high impact. Patch/upgrade should be treated as a priority for exposed or operationally important systems.

Recommended defensive actions

  • Update to V5.0 or later, as listed in the vendor remediation.
  • Review systems that may use the affected fbdev/framebuffer console mapping path and confirm whether the advisory applies.
  • Restrict local access on systems where untrusted users can reach console/framebuffer management interfaces.
  • Prioritize validation and remediation on any Siemens SIMATIC CN 4100 deployments named in the advisory.
  • Track CISA/Siemens advisory updates and confirm asset inventory against the affected product/version range.

Evidence notes

The source corpus is CISA CSAF advisory ICSA-26-134-10, republished from Siemens ProductCERT advisory SSA-032379. The advisory was initially published on 2026-05-12 and republished on 2026-05-14. The vulnerability text describes a Linux kernel fbdev fast_imageblit out-of-bounds write triggered through FBIOPUT_CON2FBMAP after a failed resize, and the supplied severity is CVSS 7.8 (HIGH).

Sources and references

Verified primary and authoritative sources

  • CVE-2025-38685 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-38685

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

  • CVE-2025-38685 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-38685

    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.