{"id":"CVE-2021-1647","kind":"vulnerability","aliases":["CVE-2021-1647"],"related":[],"title":"Microsoft Defender: Microsoft Defender Remote Code Execution Vulnerability","description":"Microsoft Defender contains an unspecified vulnerability that allows for remote code execution.\n\nCISA required action: Apply updates per vendor instructions.","summary":"Microsoft Defender (the antivirus engine) has a remote code execution flaw that CISA lists as actively exploited. An attacker who reaches the vulnerable component can run code on the machine.","severity":"critical","cvss":7.8,"epss":0.39653,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Microsoft Defender","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","microsoft-defender","other","windows"],"not_affected_if":["defender-platform-already-updated","non-windows-systems"],"how_to_check":"Check the Microsoft Defender Antimalware Platform version under Windows Security > Virus & threat protection > Protection updates, or run Get-MpComputerStatus in PowerShell and read AMProductVersion.","fix":"Update Microsoft Defender Antimalware Platform to a version at or above the fixed build in Microsoft's advisory for CVE-2021-1647; the sources do not give the build number.\nNormal Windows Update and Defender platform updates deliver the fix.","status":"open","published_at":"2021-01-12T20:15:30+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:37:24+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"other","confidence":0.6,"triage":{"at":"2026-10-23T21:37:24Z","model":"claude-haiku-5-5","output":{"fix":"Update Microsoft Defender Antimalware Platform to a version at or above the fixed build in Microsoft's advisory for CVE-2021-1647; the sources do not give the build number.\nNormal Windows Update and Defender platform updates deliver the fix.","reach":"unknown","impact":"high","summary":"Microsoft Defender (the antivirus engine) has a remote code execution flaw that CISA lists as actively exploited. An attacker who reaches the vulnerable component can run code on the machine.","category":"other","who_cares":["windows","microsoft-defender"],"confidence":0.6,"needs_auth":"unknown","worst_case":"Attacker runs arbitrary code on the affected Windows machine","analyst_note":"Find the fixed Defender platform build and attack vector in Microsoft's MSRC advisory for CVE-2021-1647 and the CISA KEV entry; sources give no affected or fixed versions.","how_to_check":"Check the Microsoft Defender Antimalware Platform version under Windows Security > Virus & threat protection > Protection updates, or run Get-MpComputerStatus in PowerShell and read AMProductVersion.\nunknown","needs_analyst":true,"not_affected_if":["non-windows-systems","defender-platform-already-updated"],"user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"critical"},"cost_usd":0.000522,"input_tokens":2808,"output_tokens":482,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-1647':11A,14A '-2021':10A,13A 'action':67C 'activ':38B 'allow':60C 'antivirus':26B 'appli':68C 'attack':41B 'cisa':35B,65C 'code':6A,31B,49B,63C 'compon':46B 'contain':55C 'cve':9A,12A 'defend':2A,4A,20B,24B,54C 'defender':16A 'engin':27B 'execut':7A,32B,64C 'exploit':17B,39B 'flaw':33B 'instruct':72C 'list':36B 'machin':52B 'microsoft':1A,3A,15A,19B,23B,53C 'microsoft-defend':18B 'per':70C 'reach':43B 'remot':5A,30B,62C 'requir':66C 'run':48B 'unspecifi':57C 'updat':69C 'vendor':71C 'vulner':8A,45B,58C 'window':22B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-01-12T20:15:30+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvss_by":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-1647","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-1647","severity":null,"published_at":"2021-11-03T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:53+00:00","fetched_at":"2026-10-25T15:39:44+00:00","note":null},{"source":"epss","external_id":"CVE-2021-1647","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-1647","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-2021-1647","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-1647","severity":null,"published_at":"2021-01-12T20:15:30+00:00","modified_at":"2026-06-17T03:32:13+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"}