{"id":"CVE-2021-38646","kind":"vulnerability","aliases":["CVE-2021-38646"],"related":[],"title":"Microsoft Office: Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability","description":"Microsoft Office Access Connectivity Engine contains an unspecified vulnerability which can allow for remote code execution.\n\nCISA required action: Apply updates per vendor instructions.","summary":"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.","severity":"high","cvss":7.8,"epss":0.07987,"exploited":true,"exploited_at":"2022-03-28T00:00:00+00:00","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"],"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).","status":"open","published_at":"2021-09-15T12:15:15+00:00","first_seen_at":"2026-10-23T19:11:52+00:00","triaged_at":"2026-10-23T21:19:48+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-23T21:19:48Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft August 2021 Office security updates per vendor instructions (sources give no exact build).\nUnknown whether a workaround exists.","reach":"unknown","impact":"high","summary":"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.","category":"infrastructure","who_cares":["microsoft-office","windows","access"],"confidence":0.6,"needs_auth":"no","worst_case":"Attacker runs code on the victim's machine via crafted document.","analyst_note":"Confirm patched build numbers and exploit delivery vector at the Microsoft advisory for CVE-2021-38646 and the CISA KEV entry.","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).\nUnknown which file or setting to inspect in sources.\nUnknown if sources give a specific registry check.","needs_analyst":true,"not_affected_if":["patched-office","office-not-installed"],"user_interaction":"yes","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000515,"input_tokens":2830,"output_tokens":464,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2021':13A,16A '-38646':14A,17A 'access':5A,20B,31B,76C 'action':92C 'activ':42B 'allow':85C 'appli':93C 'attack':59B 'catalog':53B 'cisa':45B,90C 'code':9A,37B,70B,88C 'connect':6A,32B,77C 'contain':79C 'craft':63B 'cve':12A,15A 'engin':7A,33B,78C 'execut':10A,38B,89C 'exploit':21B,43B,51B 'file':64B 'flaw':39B 'get':61B 'infrastructur':22B 'instruct':97C 'known':50B 'list':46B 'machin':73B 'microsoft':1A,3A,18A,24B,28B,74C 'microsoft-offic':23B 'note':57B 'offic':2A,4A,25B,29B,75C 'office':19A 'per':95C 'ransomwar':26B,55B 'remot':8A,36B,87C 'requir':91C 'run':69B 'unspecifi':81C 'updat':94C 'use':56B 'vendor':96C 'victim':67B 'vulner':11A,52B,82C 'window':27B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-09-15T12:15:15+00:00","kev":{"dateAdded":"2022-03-28","dueDate":"2022-04-18","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Known"},"cvss_vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","cvss_by":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-38646","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-38646","severity":null,"published_at":"2022-03-28T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:52+00:00","fetched_at":"2026-10-25T10:39:07+00:00","note":null},{"source":"epss","external_id":"CVE-2021-38646","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-38646","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-23T19:13:44+00:00","fetched_at":"2026-10-23T19:13:44+00:00","note":null},{"source":"nvd","external_id":"CVE-2021-38646","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-38646","severity":null,"published_at":"2021-09-15T12:15:15+00:00","modified_at":"2026-08-10T19:59:12+00:00","first_seen_at":"2026-10-23T21:57:35+00:00","fetched_at":"2026-10-23T21:57:35+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}