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CVE-2026-81391 Microsoft CVE debrief

Microsoft Office Excel has a vulnerability that allows local information disclosure. This CVE-2026-81391 vulnerability is caused by the use of an uninitialized resource. Defenders and IT administrators responsible for Microsoft Office installations, particularly those using Excel, should assess exposure and prioritize patching. The vulnerability has a CVSS score of 5.5 and a severity of MEDIUM. Exploitation could lead to local unauthorized access attempts. Microsoft Office Excel users should verify their versions and apply patches as needed.

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
MEDIUM 5.5
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 and IT administrators responsible for Microsoft Office installations, particularly those using Excel, should assess exposure and prioritize patching. Security teams managing Microsoft Office deployments should verify affected versions and apply patches. IT administrators should monitor for local unauthorized access attempts to Excel resources. Vulnerability management teams should prioritize patching for CV

Why it matters

CVE-2026-81391 is a medium-severity vulnerability in Microsoft Office Excel that could allow local information disclosure. Defenders and IT administrators should assess exposure, prioritize patching for affected versions, and monitor for unauthorized access attempts.

  • Local information disclosure possible through exploitation
  • Requires verification of affected versions and patch status
  • Necessitates monitoring for local unauthorized access attempts
  • Prioritization of patching for Excel and Office is crucial

Technical summary

CVE-2026-81391 is a Use of uninitialized resource vulnerability in Microsoft Office Excel. An unauthorized attacker could exploit this vulnerability to disclose information locally. The vulnerability has a CVSS score of 5.5 and a severity of MEDIUM. Affected Microsoft Office versions require verification and patching. Defenders should assess exposure and prioritize patching for Excel and Office. This vulnerability does not require complex exploitation techniques.

Defensive priority

Assess exposure, prioritize patching for Excel and Office

Recommended defensive actions

  • Inventory and assess Microsoft Office Excel installations for potential exposure
  • Prioritize and apply patches for affected Microsoft Office versions
  • Monitor for local unauthorized access attempts to Excel resources

Evidence notes

CVE-2026-81391 is a Use of uninitialized resource vulnerability in Microsoft Office Excel. The CVE Program and NVD provide official records and details.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-81391 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-81391

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

  • CVE-2026-81391 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-81391

    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.