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CVE-2026-44823 Microsoft CVE debrief

CVE-2026-44823 is a high-severity vulnerability in Microsoft Office Excel that allows unauthorized attackers to execute code locally via an integer underflow. The vulnerability has a CVSS score of 7.8 and was published on June 9, 2026. It affects various versions of Microsoft Office, including Office 2016, Office 2019, Office 2021, and Office 2024, as well as Microsoft 365 Apps. The vulnerability can be exploited when a user opens a specially crafted Excel file, allowing an attacker to execute arbitrary code on the system. Microsoft has released a vendor advisory for this vulnerability.

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

Organizations and individuals using affected versions of Microsoft Office Excel should prioritize patching this vulnerability to prevent potential code execution attacks. This includes users of Microsoft 365 Apps, Office 2016, Office 2019, Office 2021, and Office 2024.

Technical summary

CVE-2026-44823 is an integer underflow vulnerability in Microsoft Office Excel that can be exploited via a specially crafted Excel file. The vulnerability has a CVSS vector of CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H, indicating a high severity. The weakness is classified as CWE-197 and CWE-416.

Defensive priority

High

Recommended defensive actions

  • Apply the latest security updates and patches for Microsoft Office Excel and Microsoft 365 Apps.
  • Implement strict controls on file sharing and opening of Excel files from untrusted sources.
  • Use secure file transfer protocols and validate file integrity before opening.
  • Disable macros in Excel unless necessary for business operations.
  • Use a reputable antivirus solution and keep it up-to-date.
  • Conduct regular security audits and vulnerability assessments.
  • Educate users on safe computing practices and the risks of opening suspicious files.

Evidence notes

The information provided is based on data from the National Vulnerability Database (NVD) and Microsoft's vendor advisory. The CVE record and NVD detail pages provide comprehensive information on the vulnerability, including its CVSS score, affected products, and potential impacts.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-44823 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-44823

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

  • CVE-2026-44823 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-44823

    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.