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CVE-2026-78505 Microsoft CVE debrief

Microsoft Office has a heap-based buffer overflow vulnerability, classified as CWE-122, that allows unauthorized attackers to execute code over a network. This CVE was published on 2026-09-08T18:20:45.487Z and was last modified on 2026-09-17T20:18:30.867Z. The vulnerability has a CVSS score of 8.8 and is considered HIGH severity. Defenders responsible for Microsoft Office installations, particularly in enterprise and business environments, should assess exposure and apply patches or updates to mitigate this vulnerability. The affected products include various versions of Microsoft Office, including Office 2016, Office 2019, Office 2021, and Office 2024.

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
HIGH 8.8
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 installations, particularly in enterprise and business environments, should assess exposure and apply patches or updates to mitigate this vulnerability.

Why it matters

This vulnerability allows unauthorized attackers to execute code over a network, potentially leading to unauthorized access, data breaches, and disruption of business operations. Defenders should prioritize assessing exposure and applying patches for Microsoft Office, particularly for enterprise and business use cases.

  • Potential code execution over a network
  • Unauthorized access to sensitive data
  • Disruption of business operations
  • Compromise of enterprise systems

Technical summary

The CVE-2026-78505 vulnerability is a heap-based buffer overflow in Microsoft Office that allows unauthorized attackers to execute code over a network. The vulnerability has a CVSS score of 8.8 and is classified as CWE-122. The affected products include various versions of Microsoft Office, including Office 2016, Office 2019, Office 2021, and Office 2024.

Defensive priority

Defenders should prioritize assessing exposure and applying patches for Microsoft Office, particularly for enterprise and business use cases.

Recommended defensive actions

  • Assess exposure of Microsoft Office installations to this vulnerability
  • Apply patches or updates provided by Microsoft
  • Review and update incident response plans for potential code execution attacks
  • Verify network configurations to limit potential attack surfaces

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its CVSS score of 8.8 and weaknesses related to CWE-122. The official CVE Program record (CVE-2026-78505) and NVD detail page (CVE-2026-78505) offer source-provided CVE metadata and vulnerability assessments. Additional information from patch and vendor advisories (ref-3) may be necessary to fully understand the vulnerability and apply mitigations. Defenders should verify the affected scope, severity, and to

Sources and references

Verified primary and authoritative sources

  • CVE-2026-78505 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-78505

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

  • CVE-2026-78505 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-78505

    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.