PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-40361 Microsoft CVE debrief

A use-after-free vulnerability in Microsoft Office Word allows local code execution by an unauthorized attacker. The flaw, rated HIGH severity (CVSS 8.4), affects multiple Office versions including Microsoft 365 Apps Enterprise, Office 2019, Office LTSC 2021/2024 (Windows and macOS), and Word 2016. The vulnerability was published on May 12, 2026 and last modified on May 19, 2026. Microsoft has issued a vendor advisory with remediation guidance.

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
HIGH 8.4
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-12
Original CVE updated
2026-06-03
Advisory published
2026-05-12
Advisory updated
2026-06-03

Who should care

Organizations running Microsoft Office environments, particularly those with mixed-version deployments of Office 2016, 2019, 2021 LTSC, 2024 LTSC, or Microsoft 365 Apps Enterprise. Security teams responsible for endpoint protection and patch management should prioritize this vulnerability due to its high impact potential and the ubiquity of Word in enterprise document workflows.

Technical summary

The vulnerability stems from improper memory management in Microsoft Word where a use-after-free condition (CWE-416) can be triggered. The CVSS 3.1 vector (AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) indicates that while the attack vector is local, the exploitation requires no privileges or user interaction, yielding complete compromise of the affected system. The broad version scope—including both x86 and x64 architectures across Windows and macOS platforms—suggests the underlying code flaw exists in shared document parsing or rendering components.

Defensive priority

HIGH

Recommended defensive actions

  • Apply security updates from Microsoft as outlined in the vendor advisory for affected Office and Word versions
  • Prioritize patching systems running Office LTSC 2021, Office LTSC 2024, and Microsoft 365 Apps Enterprise
  • Review endpoint detection configurations for Word process anomalies indicative of memory corruption exploitation
  • Consider Microsoft Defender Application Guard or Protected View for documents from untrusted sources
  • Monitor for unexpected Word process crashes or abnormal child process spawning
  • resourceLinkAnnotations: ref-4

Evidence notes

CWE-416 (Use After Free) is the primary weakness type. CVSS vector indicates local attack vector with low attack complexity, no privileges required, and no user interaction needed—resulting in high impacts to confidentiality, integrity, and availability.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-40361 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-40361

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

  • CVE-2026-40361 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-40361

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

Supplemental references

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.