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PatchSiren cyber security CVE debrief

CVE-2025-39721 Linux CVE debrief

A use-after-free vulnerability in the Linux kernel's crypto: qat module can cause a crash when a device-specific QAT driver is repeatedly loaded and unloaded. This occurs when a power management interrupt triggers before the device-specific driver is unloaded, while the core driver remains loaded. The vulnerability is due to a shared workqueue across all devices owned by the core driver. To prevent this, the misc workqueue should be flushed during device shutdown.

Vendor
Linux
Product
SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)
CVSS
MEDIUM 4.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-14
Original CVE updated
2026-07-28
Advisory published
2026-07-14
Advisory updated
2026-07-28

Who should care

System administrators and security teams responsible for Linux kernel-based systems, particularly those using the crypto: qat module, should assess their exposure and verify the shutdown process to prevent use-after-free scenarios.

Why it matters

A use-after-free vulnerability in the Linux kernel's crypto: qat module can cause a crash when a device-specific QAT driver is repeatedly loaded and unloaded. System administrators and security teams should assess their exposure and verify the shutdown process to prevent use-after-free scenarios.

  • Verify the shutdown process to prevent use-after-free scenarios.
  • Assess exposure and apply recommended mitigations.
  • Monitor system stability and correctness during shutdown.
  • Verify versions and configurations of affected products.

Technical summary

The Linux kernel's crypto: qat module is vulnerable to a use-after-free scenario due to a shared workqueue across all devices owned by the core driver. This can cause a crash when a device-specific QAT driver is repeatedly loaded and unloaded. The vulnerability is due to a shared workqueue across all devices owned by the core driver. To prevent this, the misc workqueue should be flushed during device shutdown to ensure that no pending routines execute after the driver is unloaded, which can dereference freed memory and result in a page fault and kernel crash.

Defensive priority

Medium

Recommended defensive actions

  • Review and apply the recommended mitigations provided by the vendor, such as limiting access to the interactive shell and building applications from trusted sources.
  • Flush the misc workqueue during device shutdown to prevent use-after-free scenarios.
  • Monitor and verify the shutdown process to ensure correctness and stability.
  • Verify versions and configurations of affected products.
  • Assess exposure and apply recommended mitigations.
  • Monitor system stability and correctness during shutdown.
  • Review compensating controls for exposed systems while remediation is scheduled and verified.

Evidence notes

The CVE record and source item provide details about the vulnerability, its impact, and potential mitigations. However, the corpus does not establish versions, exploitation, impact, or remediation for all affected products, requiring verification from official sources.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-39721 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-39721

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

  • CVE-2025-39721 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2025-39721

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • CVE-2025-39721

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/OT/white/2026/icsa-26-209-04.json

    cisa_csaf

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/csaf/ssa-019113.json

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://cert-portal.siemens.com/productcert/html/ssa-019113.html

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-advisories/icsa-26-209-04

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/news-events/ics-alerts/ics-alert-10-301-01

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/resources-tools/resources/ics-recommended-practices

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/topics/industrial-control-systems

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/recommended_practices/NCCIC_ICS-CERT_Defense_in_Depth_2016_S508C.pdf

    Supplemental source

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.