{"id":"CVE-2021-31956","kind":"vulnerability","aliases":["CVE-2021-31956"],"related":[],"title":"Microsoft Windows: Microsoft Windows NTFS Privilege Escalation Vulnerability","description":"Microsoft Windows New Technology File System (NTFS) contains an unspecified vulnerability that allows attackers to escalate privileges via a specially crafted application.\n\nCISA required action: Apply updates per vendor instructions.","summary":"Microsoft Windows NTFS, the file system driver, has an unspecified flaw that lets a crafted application raise its privileges. An attacker who can run code on the machine can gain higher privileges, and CISA lists it as exploited in the wild.","severity":"critical","cvss":9.3,"epss":0.22273,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Microsoft Windows","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","infrastructure","windows"],"not_affected_if":["non-windows"],"how_to_check":null,"fix":"Apply the Microsoft update for CVE-2021-31956 per vendor instructions (CISA KEV required action).","status":"open","published_at":"2021-06-08T23:15:08+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:43:30+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"infrastructure","confidence":0.7,"triage":{"at":"2026-10-23T21:43:30Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft update for CVE-2021-31956 per vendor instructions (CISA KEV required action).\nunknown","reach":"local","impact":"high","summary":"Microsoft Windows NTFS, the file system driver, has an unspecified flaw that lets a crafted application raise its privileges. An attacker who can run code on the machine can gain higher privileges, and CISA lists it as exploited in the wild.","category":"infrastructure","who_cares":["windows"],"confidence":0.7,"needs_auth":"yes","worst_case":"local user gains SYSTEM privileges on the Windows machine","analyst_note":"Find the Microsoft advisory and the affected Windows build numbers and KB update for CVE-2021-31956 to fill in how_to_check and the exact fix.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["non-windows"],"user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000456,"input_tokens":2836,"output_tokens":344,"severity_before":"unknown"},"analyst_status":"queued","analyst_note":"Find the Microsoft advisory and the affected Windows build numbers and KB update for CVE-2021-31956 to fill in how_to_check and the exact fix.","search":"'-2021':10A,13A '-31956':11A,14A 'action':85C 'allow':73C 'appli':86C 'applic':35B,82C 'attack':40B,74C 'cisa':53B,83C 'code':44B 'contain':68C 'craft':34B,81C 'cve':9A,12A 'driver':26B 'escal':7A,76C 'exploit':17B,57B 'file':24B,65C 'flaw':30B 'gain':49B 'higher':50B 'infrastructur':18B 'instruct':90C 'let':32B 'list':54B 'machin':47B 'microsoft':1A,3A,15A,20B,61C 'new':63C 'ntfs':5A,22B,67C 'per':88C 'privileg':6A,38B,51B,77C 'rais':36B 'requir':84C 'run':43B 'special':80C 'system':25B,66C 'technolog':64C 'unspecifi':29B,70C 'updat':87C 'vendor':89C 'via':78C 'vulner':8A,71C 'wild':60B 'window':2A,4A,19B,21B,62C 'windows':16A","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-06-08T23:15:08+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-2021-31956","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-31956","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":"2026-10-25T14:39:41+00:00","note":null},{"source":"epss","external_id":"CVE-2021-31956","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-31956","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-2021-31956","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-31956","severity":null,"published_at":"2021-06-08T23:15:08+00:00","modified_at":"2026-06-17T03:52:33+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"}