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PatchSiren cyber security CVE debrief

CVE-2026-81398 Microsoft CVE debrief

Microsoft Office Excel is vulnerable to a heap-based buffer overflow, allowing an unauthorized attacker to execute code locally. The CVE record was published on 2026-09-08T18:20:56.437Z and has not been modified since then. The NVD entry is currently Analyzed. This vulnerability affects Microsoft Office Excel installations, which defenders should assess for exposure and prioritize patching to prevent local code execution. The vulnerability has a CVSS score of 7.8 and is classified as HIGH.

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-08
Original CVE updated
2026-09-17
Advisory published
2026-09-08
Advisory updated
2026-09-17

Who should care

Defenders responsible for Microsoft Office Excel installations should assess exposure and prioritize patching to prevent local code execution.

Why it matters

Defenders should prioritize patching vulnerable Microsoft Office Excel installations to prevent local code execution. The vulnerability has a CVSS score of 7.8 and is classified as HIGH.

  • Potential for local code execution
  • Need for patching vulnerable installations
  • Verification of Microsoft's vendor advisory

Technical summary

A heap-based buffer overflow vulnerability exists in Microsoft Office Excel, allowing an unauthorized attacker to execute code locally. The vulnerability has a CVSS score of 7.8 and is classified as HIGH. This vulnerability is particularly concerning for defenders responsible for Microsoft Office Excel installations, as it could allow attackers to execute code locally without authorization.

Defensive priority

Defenders should prioritize patching vulnerable Microsoft Office Excel installations to prevent local code execution.

Recommended defensive actions

  • Patch vulnerable Microsoft Office Excel installations
  • Verify and apply Microsoft's vendor advisory
  • Monitor for unauthorized access to Microsoft Office Excel

Evidence notes

The CVE record and NVD detail page provide information on the vulnerability, but do not specify affected or fixed versions. Microsoft has provided a patch and vendor advisory.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-81398 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-81398

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

  • CVE-2026-81398 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-81398

    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.