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CVE-2026-55018 Microsoft CVE debrief

CVE-2026-55018 is a high-severity vulnerability in Microsoft Office, allowing unauthorized attackers to execute code locally. The vulnerability has a CVSS score of 7.8 and is classified as HIGH. It was published on 2026-07-14T18:18:12.287Z and last modified on 2026-07-16T15:22:31.510Z. This use-after-free issue in Microsoft Office requires immediate attention from users of Microsoft 365 Apps, Office 2016, Office 2019, Office 2021, and Office 2024. The vulnerability's CVSS vector is CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H, classified under CWE-416.

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-14
Original CVE updated
2026-07-16
Advisory published
2026-07-14
Advisory updated
2026-07-16

Who should care

Users of Microsoft Office, particularly those using Microsoft 365 Apps, Office 2016, Office 2019, Office 2021, and Office 2024, should be aware of this vulnerability and take necessary precautions. This includes reviewing and applying patches provided by Microsoft, ensuring all Microsoft Office applications are up-to-date, and implementing compensating controls such as monitoring for suspicious activity.

Technical summary

The vulnerability is a use-after-free issue in Microsoft Office, which allows an unauthorized attacker to execute code locally. The CVSS vector is CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. The weakness is classified as CWE-416. This issue affects Microsoft Office, particularly Microsoft 365 Apps, Office 2016, Office 2019, Office 2021, and Office 2024. Users should ensure their applications are up-to-date and consider implementing compensating controls.

Defensive priority

High

Recommended defensive actions

  • Apply the patch provided by Microsoft
  • Ensure all Microsoft Office applications are up-to-date
  • Implement compensating controls, such as monitoring for suspicious activity
  • Conduct regular inventory checks to ensure all systems are patched
  • Consider implementing additional security measures, such as network segmentation

Evidence notes

The CVE record was published on 2026-07-14T18:18:12.287Z and was last modified on 2026-07-16T15:22:31.510Z. The NVD entry is currently Analyzed. This vulnerability affects Microsoft Office, particularly Microsoft 365 Apps, Office 2016, Office 2019, Office 2021, and Office 2024. Users should verify their deployments and ensure they are up-to-date. The CVE details are sourced from CVE.org and NVD.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-55018 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-55018

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

  • CVE-2026-55018 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-55018

    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.