{"id":"CVE-2021-34527","kind":"vulnerability","aliases":["CVE-2021-34527"],"related":[],"title":"Microsoft Windows: Microsoft Windows Print Spooler Remote Code Execution Vulnerability","description":"A remote code execution vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.\nUPDATE July 7, 2021: The security update for Windows Server 2012, Windows Server 2016 and Windows 10, Version 1607 have been released. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability.\nIn addition to installing the updates, in order to secure your system, you must confirm that the following registry settings are set to 0 (zero) or are not defined (Note: These registry keys do not exist by default, and therefore are already at the secure setting.), also that your Group Policy setting are correct (see FAQ):\n\nHKEY_LOCAL_MACHINE\\SOFTWARE\\Policies\\Microsoft\\Windows NT\\Printers\\PointAndPrint\nNoWarningNoElevationOnInstall = 0 (DWORD) or not defined (default setting)\nUpdatePromptSettings = 0 (DWORD) or not defined (default setting)\n\nHaving NoWarningNoElevationOnInstall set to 1 makes your system vulnerable by design.\nUPDATE July 6, 2021: Microsoft has completed the investigation and has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. See also KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates.\nNote that the security updates released on and after July 6, 2021 contain protections for CVE-2021-1675 and the additional remote code execution exploit in the Windows Print Spooler service known as “PrintNightmare”, documented in CVE-2021-34527.","summary":"The Windows Print Spooler service improperly performs privileged file operations, known as PrintNightmare. An attacker can run code as SYSTEM on the Windows machine, and CISA lists it as actively exploited with ransomware use.","severity":"critical","cvss":9.0,"epss":0.99792,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Microsoft Windows","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["active-directory","exploited","infrastructure","print-server","ransomware","windows"],"not_affected_if":["print-spooler-disabled"],"how_to_check":null,"fix":"Apply the Microsoft update for CVE-2021-34527 per vendor instructions (CISA KEV required action). Exact patched build numbers are not in the sources.","status":"open","published_at":"2021-07-02T22:15:08+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:39:17+00:00","updated_at":"2026-10-23T21:57:34+00:00","category":"infrastructure","confidence":0.7,"triage":{"at":"2026-10-23T21:39:17Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft update for CVE-2021-34527 per vendor instructions (CISA KEV required action). Exact patched build numbers are not in the sources.","reach":"network","impact":"high","summary":"The Windows Print Spooler service improperly performs privileged file operations, known as PrintNightmare. An attacker can run code as SYSTEM on the Windows machine, and CISA lists it as actively exploited with ransomware use.","category":"infrastructure","who_cares":["windows","print-server","active-directory"],"confidence":0.7,"needs_auth":"unknown","worst_case":"Attacker runs code as SYSTEM, taking over the Windows machine","analyst_note":"Find the Microsoft Security Response Center advisory for CVE-2021-34527 to confirm affected builds, patched KBs, and whether remote unauthenticated exploitation applies or only authenticated domain users.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["print-spooler-disabled"],"user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"critical"},"cost_usd":0.000485,"input_tokens":2895,"output_tokens":391,"severity_before":"unknown"},"analyst_status":"queued","analyst_note":"Find the Microsoft Security Response Center advisory for CVE-2021-34527 to confirm affected builds, patched KBs, and whether remote unauthenticated exploitation applies or only authenticated domain users.","search":"'-1675':379C '-2021':12A,15A,378C,399C '-34527':13A,16A,400C '0':208C,252C,260C '1':271C '10':129C '1607':131C '2012':123C '2016':126C '2021':116C,281C,360C,373C '6':280C,359C,372C '7':115C 'account':108C 'activ':20B,58B 'active-directori':19B 'addit':186C,382C 'address':293C 'alreadi':226C 'also':231C,347C 'appli':356C 'applic':143C,304C 'arbitrari':89C 'attack':43B,81C,95C 'chang':101C 'cisa':54B 'code':8A,46B,65C,90C,384C 'complet':284C 'confirm':199C 'contain':374C 'correct':238C 'could':87C,96C 'creat':106C 'cve':11A,14A,172C,333C,377C,398C 'data':104C 'default':222C,257C,265C 'defin':213C,256C,264C 'delet':103C 'design':277C 'directori':21B 'document':396C 'driver':354C 'dword':253C,261C 'execut':9A,66C,385C 'exist':68C,220C 'exploit':22B,59B,84C,386C 'faq':166C,240C,327C 'file':37B,78C 'follow':202C 'full':110C 'group':234C 'help':178C,339C 'hkey':241C 'immedi':155C,316C 'improp':34B,75C 'inform':174C,335C 'infrastructur':23B 'instal':98C,152C,161C,188C,313C,322C,350C 'investig':286C 'juli':114C,279C,358C,371C 'kb5005010':348C 'key':217C 'known':39B,393C 'list':55B 'local':242C 'machin':52B,243C 'make':272C 'microsoft':1A,3A,17A,246C,282C 'must':198C 'new':107C,352C 'note':214C,362C 'nowarningnoelevationoninstal':251C,268C 'nt':248C 'oper':38B,79C 'order':192C 'perform':35B,76C 'pleas':135C,296C 'pointandprint':250C 'polici':235C,245C 'print':5A,25B,31B,72C,390C 'print-serv':24B 'printer':249C,353C 'printnightmar':41B,395C 'privileg':36B,77C,93C 'program':99C 'protect':179C,340C,375C 'ransomwar':27B,61B 'recommend':149C,310C 'registri':203C,216C 'releas':134C,289C,367C 'remot':7A,64C,383C 'restrict':349C 'right':112C 'run':45B,88C 'section':169C,330C 'secur':118C,138C,194C,229C,290C,299C,365C 'see':136C,164C,239C,297C,325C,346C 'server':26B,122C,125C 'servic':33B,74C,392C 'set':204C,206C,230C,236C,258C,266C,269C 'softwar':244C 'spooler':6A,32B,73C,391C 'success':83C 'system':48B,92C,147C,181C,196C,274C,308C,342C 'tabl':140C,301C 'therefor':224C 'unabl':159C,320C 'updat':113C,119C,139C,144C,154C,163C,190C,278C,291C,300C,305C,315C,324C,361C,366C 'updatepromptset':259C 'use':62B 'user':111C 'version':130C 'view':100C 'vulner':10A,67C,86C,184C,275C,295C,345C 'window':2A,4A,28B,30B,51B,71C,121C,124C,128C,247C,389C 'windows':18A 'workaround':168C,329C 'zero':209C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-07-02T22:15:08+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2022-05-03","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Known"},"cvss_vector":"CVSS:3.1/AV:N/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-2021-34527","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-34527","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":"2026-10-25T11:39:18+00:00","note":null},{"source":"epss","external_id":"CVE-2021-34527","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-34527","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-2021-34527","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-34527","severity":null,"published_at":"2021-07-02T22:15:08+00:00","modified_at":"2026-08-10T20:15:22+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","fetched_at":"2026-10-23T21:57:34+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"}