---
id: "CVE-2021-38646"
kind: "vulnerability"
aliases: ["CVE-2021-38646"]
title: "Microsoft Office: Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability"
severity: "high"
cvss: 7.8
epss: 0.07987
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Microsoft Office", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["access", "exploited", "infrastructure", "microsoft-office", "ransomware", "windows"]
not_affected_if: ["office-not-installed", "patched-office"]
published_at: "2021-09-15T12:15:15+00:00"
first_seen_at: "2026-10-23T19:11:52+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-38646", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-38646", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-38646", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Microsoft Office: Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability

Microsoft Office's Access Connectivity Engine has a remote code execution flaw that is actively exploited, and CISA lists it in its Known Exploited Vulnerabilities catalog with ransomware use noted. An attacker who gets a crafted file to a victim can run code on that machine.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Microsoft Office affected ? fixed ?

## How to check

Check the installed Office build against Microsoft's August 2021 security update for CVE-2021-38646 (unknown exact build numbers in sources).

## Fix

Apply the Microsoft August 2021 Office security updates per vendor instructions (sources give no exact build).

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-38646
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-38646
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-38646

## From the sources

Microsoft Office Access Connectivity Engine contains an unspecified vulnerability which can allow for remote code execution.

CISA required action: Apply updates per vendor instructions.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_