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PatchSiren cyber security CVE debrief

CVE-2025-39737 Siemens CVE debrief

CVE-2025-39737 is an availability issue in the Linux kernel’s kmemleak cleanup path. According to the supplied advisory text, disabling kmemleak after object-allocation failure can leave __kmemleak_do_cleanup() processing a very large number of objects one by one, which can monopolize CPU time and trigger a soft lockup. The source corpus ties the CVE to Siemens advisory ICSA-26-134-10 / SSA-032379 and maps it to Siemens SIMATIC CN 4100 versions before 5.0, with a CVSS v3.1 score of 5.5 (Medium).

Vendor
Siemens
Product
SIMATIC CN 4100
CVSS
MEDIUM 5.5
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

Administrators and operators who rely on the Siemens advisory scope in the source corpus (SIMATIC CN 4100 versions before 5.0), plus Linux kernel maintainers and test/debug environments that enable kmemleak and watchdog monitoring.

Technical summary

The reported condition occurs in mm/kmemleak when kmemleak is disabled after it cannot allocate more kmemleak objects. Cleanup then iterates through many existing objects in __kmemleak_do_cleanup(), deleting them individually via a workqueue. On a debug kernel with a large kmemleak object pool, the repeated per-object work and locking can run long enough to cause a soft lockup warning. The supplied description says the fix is to add periodic cond_resched() calls during iteration so the kernel can yield and avoid the lockup.

Defensive priority

Medium. The impact is availability-only and appears limited to systems that hit the kmemleak-disabled cleanup path, but the supplied advisory still assigns CVSS 5.5 and recommends remediation.

Recommended defensive actions

  • Apply the vendor remediation in the source corpus: update to V5.0 or later for the affected Siemens product scope.
  • Treat the issue as an availability risk in debug, test, or maintenance environments where kmemleak is enabled.
  • Watch for watchdog soft lockup messages and unusual delays in kmemleak cleanup on affected systems.
  • Review whether kmemleak-enabled debug configurations are present in environments that should not run them.
  • Use the Siemens and CISA advisory links in the source corpus to confirm the exact product scope before scheduling remediation.

Evidence notes

The source corpus contains a Linux-kernel-style fix description for kmemleak cleanup, while the advisory metadata maps the CVE to Siemens SIMATIC CN 4100 vers:intdot/<5.0. That product association is explicitly marked low confidence / needs review in the provided data, so the product mapping should be validated against the linked Siemens and CISA advisories. The corpus also states CVSS v3.1 5.5 (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-2025-39737 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-39737

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

  • CVE-2025-39737 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-39737

    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.