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CVE-2026-44820 Microsoft CVE debrief

CVE-2026-44820 is a HIGH-severity vulnerability in Microsoft Office Excel, with a CVSS score of 7.8. The vulnerability is caused by an integer underflow (wrap or wraparound) and allows an unauthorized attacker to execute code locally. The vulnerability was published on 2026-06-09T17:17:18.313Z and last modified on 2026-06-11T18:38:16.130Z.

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-09
Original CVE updated
2026-07-09
Advisory published
2026-06-09
Advisory updated
2026-07-09

Who should care

Users of Microsoft Office Excel, particularly those who open Excel files from untrusted sources, should be aware of this vulnerability and take steps to mitigate it.

Technical summary

The vulnerability is caused by an integer underflow (wrap or wraparound) in Microsoft Office Excel. This allows an attacker to execute code locally, potentially leading to a compromise of the system.

Defensive priority

HIGH

Recommended defensive actions

  • Apply patches or updates from Microsoft as soon as possible.
  • Be cautious when opening Excel files from untrusted sources.
  • Use antivirus software and keep it up to date.

Evidence notes

The vulnerability is described in the CVE record [cve-org] and detailed in the NVD entry [nvd]. Microsoft has also provided a vendor advisory [ref-4].

Sources and references

Verified primary and authoritative sources

  • CVE-2026-44820 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-44820

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

  • CVE-2026-44820 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-44820

    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.