# CVE-2026-55018 — Microsoft 365 Apps for Enterprise

> As of 2026-10-08, CVE-2026-55018 is a HIGH-severity vulnerability in Microsoft 365 Apps for Enterprise, CVSS v3.1 7.8, EPSS 0.4% (38.4th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-55018, most recently “Microsoft July 2026 Patch Tuesday: 570 Flaws Fixed, 3 Zero-Days Including AD FS and SharePoint Privilege Escalation”.

**Last updated:** 2026-10-08

## What is CVE-2026-55018?

Use after free in Microsoft Office allows an unauthorized attacker to execute code locally.

The record classifies CVE-2026-55018 under weakness class [CWE-416](https://intel.threadlinqs.com/cwe/CWE-416). Its CVSS v3 base vector states that the flaw requires local access to the host, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity, availability. 8 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 106 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.8 — HIGH (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **EPSS (FIRST):** 0.4% probability of exploitation in the next 30 days, higher than 38.4% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-14, last modified 2026-10-08

## Is CVE-2026-55018 being exploited?

It currently carries a trending score of 23 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [Microsoft](https://intel.threadlinqs.com/vendors/microsoft): 365 Apps for Enterprise, Office 2016, Office 2019, Office 365 for Mac, Office LTSC 2021, Office LTSC 2024, Office LTSC for Mac 2021, Office LTSC for Mac 2024

## How to fix CVE-2026-55018

The record marks a vendor fix as available for CVE-2026-55018. Patch reference: [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55018](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55018). Vendor advisory: [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55018](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55018). Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

## Threat activity tracking CVE-2026-55018

1 tracked threat in the Threadlinqs corpus references CVE-2026-55018, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Microsoft July 2026 Patch Tuesday: 570 Flaws Fixed, 3 Zero-Days Including AD FS and SharePoint Privilege Escalation](https://intel.threadlinqs.com/threat/TL-2026-1324) — CRITICAL · 2026-07-14

## Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [msrc.microsoft.com — vendor advisory](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55018)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-55018
Full detection coverage and IOCs for threats exploiting CVE-2026-55018 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp