{"id":"CVE-2021-34527","published":"2021-07-02T22:15:08Z","modified":"2026-08-10T20:15:22Z","title":"Microsoft Windows Print Spooler Remote Code Execution Vulnerability","vendor":"Microsoft","product":"Windows","tier":"core","eol":null,"description":{"text":"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.","provenance":"source","from":"NVD"},"summary":{"text":"A flaw in the Windows Print Spooler service on Microsoft Windows improperly performs privileged file operations, which can allow remote code execution. An attacker with low-privilege authenticated access over the network, requiring no user interaction, could run arbitrary code with SYSTEM privileges and then install programs, view, change or delete data, or create accounts with full user rights.","provenance":"ai","model":"claude-haiku-5-5","generatedAt":"2026-10-23T06:54:07Z"},"cvss":{"score":8.8,"severity":"HIGH","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","provenance":"source","from":"NVD"},"epss":{"score":0.99792,"percentile":0.99956,"date":"2026-10-30","provenance":"source"},"kev":{"dateAdded":"2021-11-03","dueDate":"2022-05-03","ransomware":true,"requiredAction":"Apply updates per vendor instructions.","notes":"Reference CISA's ED 21-04 (https://www.cisa.gov/news-events/directives/ed-21-04-mitigate-windows-print-spooler-service-vulnerability) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-04. https://nvd.nist.gov/vuln/detail/CVE-2021-34527","provenance":"source"},"vulncheckKev":{"dateAdded":"2021-07-02","exploitedFirstSeen":"2021-07-02","ransomware":true,"evidence":[{"url":"https://api.msrc.microsoft.com/cvrf/v3.0/cvrf/2021-Jul","date":"2021-07-02"},{"url":"https://www.fortinet.com/blog/threat-research/affiliates-cookbook-firsthand-peek-into-operations-and-tradecraft-of-conti","date":"2021-08-10"},{"url":"https://www.crowdstrike.com/blog/magniber-ransomware-caught-using-printnightmare-vulnerability/","date":"2021-08-11"},{"url":"https://blog.talosintelligence.com/2021/08/vice-society-ransomware-printnightmare.html","date":"2021-08-12"},{"url":"https://us-cert.cisa.gov/ncas/alerts/aa21-265a","date":"2021-09-22"},{"url":"https://www.cybereason.com/blog/threat-analysis-report-printnightmare-and-magniber-ransomware","date":"2021-09-22"},{"url":"https://blog.qualys.com/product-tech/2021/10/05/assess-risk-ransomware-attacks-qualys-research","date":"2021-10-05"},{"url":"https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json","date":"2021-11-03"},{"url":"https://cybersecurityworks.com/howdymanage/uploads/file/csw_final_ransomware_index-update-q321-csw_.pdf","date":"2021-11-10"},{"url":"https://www.advintel.io/post/ransomware-advisory-log4shell-exploitation-for-initial-access-lateral-movement","date":"2021-12-17"}],"evidenceTotal":60,"provenance":"source"},"exploited":true,"otx":{"pulseCount":50,"pulses":[{"name":"Actively_Exploited_Kev | Oct 29, 2026","url":"https://otx.alienvault.com/pulse/6ae20c1db17e7057ae7d9ad1","created":"2026-10-28"},{"name":"Actively_Exploited_Kev | Oct 28, 2026","url":"https://otx.alienvault.com/pulse/6ae0ba7e0e2a97ff7b218819","created":"2026-10-27"},{"name":"Actively_Exploited_Kev | Oct 27, 2026","url":"https://otx.alienvault.com/pulse/6adf68b85c3e852f3c111d18","created":"2026-10-26"},{"name":"Actively_Exploited_Kev | Oct 24, 2026","url":"https://otx.alienvault.com/pulse/6adb740e397c3ad4799aa4cd","created":"2026-10-23"},{"name":"Actively_Exploited_Kev | Oct 23, 2026","url":"https://otx.alienvault.com/pulse/6ada236fcfba2dfa730ea482","created":"2026-10-22"},{"name":"Actively_Exploited_Kev | Oct 22, 2026","url":"https://otx.alienvault.com/pulse/6ad8d33a077cbb5cab524d80","created":"2026-10-21"},{"name":"Actively_Exploited_Kev | Oct 21, 2026","url":"https://otx.alienvault.com/pulse/6ad78130c4d1ac2be83a8b6d","created":"2026-10-20"},{"name":"Actively_Exploited_Kev | Oct 20, 2026","url":"https://otx.alienvault.com/pulse/6ad62f63c24a405a3423cc13","created":"2026-10-19"},{"name":"Actively_Exploited_Kev | Oct 19, 2026","url":"https://otx.alienvault.com/pulse/6ad4dda174e5797d0bd238b7","created":"2026-10-18"},{"name":"Actively_Exploited_Kev | Oct 18, 2026","url":"https://otx.alienvault.com/pulse/6ad38c22e1848f8189d1c121","created":"2026-10-17"}],"provenance":"machine"},"cwes":[{"id":"CWE-269","name":"Improper Privilege Management"}],"references":[{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34527","tags":["Patch","Vendor Advisory"]},{"url":"http://packetstormsecurity.com/files/167261/Print-Spooler-Remote-DLL-Injection.html","tags":["Exploit","Third Party Advisory","VDB Entry"]},{"url":"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34527","tags":["Mitigation","Patch","Vendor Advisory"]},{"url":"https://www.kb.cert.org/vuls/id/383432","tags":["Third Party Advisory","US Government Resource"]},{"url":"https://www.vicarius.io/vsociety/posts/cve-2021-34527-printnightmare-detection-script","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.vicarius.io/vsociety/posts/cve-2021-34527-printnightmare-mitigation-script","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34527","tags":["US Government Resource"]}],"techniques":[{"id":"T1068","name":"Exploitation for Privilege Escalation","tactics":["privilege-escalation"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping","dataset-annotation"],"basisDetail":"claude-haiku-5-5: Print Spooler privilege flaw enables local escalation; TRAM2 annotated sentence label","mappingType":"exploitation_technique","evidence":[{"from":"description","quote":"improperly performs privileged file operations","start":84,"end":130},{"reportId":"SRC-6fd50dda970234534055","quote":"Software vulnerabilities, such as PrintNightmare (CVE-2021-1675) and (CVE-2021-34527), may be exploited in an attempt to elevate privileges.","start":17385,"end":17525}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"},{"id":"T1059","name":"Command and Scripting Interpreter","tactics":["execution"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Arbitrary code execution as SYSTEM","mappingType":"primary_impact","evidence":[{"from":"description","quote":"could run arbitrary code with SYSTEM privileges","start":190,"end":237}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"},{"id":"T1190","name":"Exploit Public-Facing Application","tactics":["initial-access"],"provenance":"machine","basis":"dataset-annotation","bases":["dataset-annotation"],"basisDetail":"TRAM2 annotated sentence label","mappingType":null,"evidence":[{"reportId":"SRC-6fd50dda970234534055","quote":"Internet-facing applications and systems vulnerabilities can be exploited, such as PrintNightmare (CVE-2021-1675) and (CVE-2021-34527), to gain initial access.","start":16192,"end":16351}],"confidence":"low","confidenceNote":"machine-matched from report text"},{"id":"T1210","name":"Exploitation of Remote Services","tactics":["lateral-movement"],"provenance":"machine","basis":"dataset-annotation","bases":["dataset-annotation"],"basisDetail":"TRAM2 annotated sentence label","mappingType":null,"evidence":[{"reportId":"SRC-61bedc5e767b65113ffd","quote":"Joe Marshall, and Arnaud Zobec.Executive SummaryAnother threat actor is actively exploiting the so-called PrintNightmare vulnerability (CVE-2021-1675 / CVE-2021-34527) in Windows' print spooler service to spread laterally across a victim's network as part of a recent ransomware attack, according to Cisco Talos","start":181,"end":492}],"confidence":"low","confidenceNote":"machine-matched from report text"}],"reports":[{"id":"SRC-981a72220ddd35764116","title":"Bumblebee: New Loader Rapidly Assuming Central Position in Cyber-crime Ecosystem","publisher":"security.com","url":"https://www.security.com/threat-intelligence/bumblebee-loader-cybercrime","date":null,"mentions":[{"quote":"The attackers also made use of a PowerShell script named cve-2021-34527.ps1 that has previously been linked to Conti’s leaked attack playbook.","start":5442,"end":5584}]},{"id":"SRC-6fd50dda970234534055","title":"Vice Society: Profiling a Persistent Threat to the Education Sector","publisher":"unit42.paloaltonetworks.com","url":"https://unit42.paloaltonetworks.com/vice-society-targets-education-sector/","date":null,"mentions":[{"quote":"Vice Society first surfaced in the summer of 2021, and in that time frame it was seen exploiting the CVE-2021-34527 (aka PrintNightmare) vulnerability as part of their attack chain.","start":1099,"end":1280},{"quote":"Internet-facing applications and systems vulnerabilities can be exploited, such as PrintNightmare (CVE-2021-1675) and (CVE-2021-34527), to gain initial access.","start":16192,"end":16351},{"quote":"Software vulnerabilities, such as PrintNightmare (CVE-2021-1675) and (CVE-2021-34527), may be exploited in an attempt to elevate privileges.","start":17385,"end":17525},{"quote":"Resources\nThreat Brief: Windows Print Spooler RCE Vulnerability (CVE-2021-34527 AKA PrintNightmare)Emerging Ransomware Groups: AvosLocker, Hive, HelloKitty, LockBit 2.0Threat Assessment: Zeppelin Ransomware#StopRansomware: Vice","start":22486,"end":22713}]},{"id":"SRC-61bedc5e767b65113ffd","title":"Vice Society leverages PrintNightmare in ransomware attacks","publisher":"blog.talosintelligence.com","url":"https://blog.talosintelligence.com/2021/08/vice-society-ransomware-printnightmare.html","date":null,"mentions":[{"quote":"Joe Marshall, and Arnaud Zobec.Executive SummaryAnother threat actor is actively exploiting the so-called PrintNightmare vulnerability (CVE-2021-1675 / CVE-2021-34527) in Windows' print spooler service to spread laterally across a victim's network as part of a recent ransomware attack, according to Cisco Talos","start":181,"end":492}]},{"id":"SRC-06a2fa5397da4000010a","title":"ICS/OT CYBERSECURITY","publisher":"hub.dragos.com","url":"https://hub.dragos.com/hubfs/333%20Year%20in%20Review/2021/2021%20ICS%20OT%20Cybersecurity%20Year%20In%20Review%20-%20Dragos%202021.pdf?hsLang=en","date":null,"mentions":[{"quote":"Adversaries can leverage PrintNightmare CVE-2021-34527, CVE-2021-34481, and","start":95816,"end":95891}]}],"affected":[],"advisories":[],"euvd":{"id":"EUVD-2021-21181","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-21181","exploited":true,"exploitedSince":"2021-11-03","provenance":"source"},"exploits":[],"exploitSources":{"pocGithub":{"count":28,"skipped":2,"earliest":"2021-07-01","earliestUrl":"https://github.com/DenizSe/CVE-2021-34527","repos":[{"name":"byt3bl33d3r/ItWasAllADream","url":"https://github.com/byt3bl33d3r/ItWasAllADream","stars":802,"created":"2021-07-05"},{"name":"JohnHammond/CVE-2021-34527","url":"https://github.com/JohnHammond/CVE-2021-34527","stars":326,"created":"2021-07-02"},{"name":"nemo-wq/PrintNightmare-CVE-2021-34527","url":"https://github.com/nemo-wq/PrintNightmare-CVE-2021-34527","stars":179,"created":"2021-07-03"},{"name":"m8sec/CVE-2021-34527","url":"https://github.com/m8sec/CVE-2021-34527","stars":119,"created":"2022-08-23"},{"name":"hackerhouse-opensource/cve-2021-34527","url":"https://github.com/hackerhouse-opensource/cve-2021-34527","stars":23,"created":"2022-09-05"}]},"metasploit":[{"name":"Print Spooler Remote DLL Injection","module":"exploit/windows/dcerpc/cve_2021_1675_printnightmare","type":"exploit","disclosureDate":"2021-06-08","url":"https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/dcerpc/cve_2021_1675_printnightmare.rb"}],"first":{"date":"2021-06-08","source":"Metasploit","url":"https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/dcerpc/cve_2021_1675_printnightmare.rb"},"provenance":"source"},"detections":{"cveRules":[{"title":"Antivirus PrinterNightmare CVE-2021-34527 Exploit Detection","id":"6fe1719e-ecdf-4caf-bffe-4f501cb0a561","level":"critical","status":"stable","path":"rules-emerging-threats/2021/Exploits/CVE-2021-1675/av_exploit_cve_2021_34527_print_nightmare.yml","url":"https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-1675/av_exploit_cve_2021_34527_print_nightmare.yml","techniques":["T1055"]},{"title":"CVE-2021-1675 Print Spooler Exploitation IPC Access","id":"8fe1c584-ee61-444b-be21-e9054b229694","level":"critical","status":"test","path":"rules-emerging-threats/2021/Exploits/CVE-2021-1675/win_security_exploit_cve_2021_1675_printspooler_security.yml","url":"https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-1675/win_security_exploit_cve_2021_1675_printspooler_security.yml","techniques":["T1569"]},{"title":"PrinterNightmare Mimikatz Driver Name","id":"ba6b9e43-1d45-4d3c-a504-1043a64c8469","level":"critical","status":"test","path":"rules-emerging-threats/2021/Exploits/CVE-2021-1675/registry_event_cve_2021_1675_mimikatz_printernightmare_drivers.yml","url":"https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-1675/registry_event_cve_2021_1675_mimikatz_printernightmare_drivers.yml","techniques":["T1204"]},{"title":"Possible PrintNightmare Print Driver Install - CVE-2021-1675","id":"7b33baef-2a75-4ca3-9da4-34f9a15382d8","level":"medium","status":"stable","path":"rules-emerging-threats/2021/Exploits/CVE-2021-1675/zeek_dce_rpc_exploit_cve_2021_1675_printnightmare_print_driver_install.yml","url":"https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-1675/zeek_dce_rpc_exploit_cve_2021_1675_printnightmare_print_driver_install.yml","techniques":[]},{"title":"Windows Spooler Service Suspicious Binary 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exploited","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-21181","provenance":"source"}],"speed":{"daysToPublicExploit":null,"firstExploitFrom":"Metasploit","daysToKev":124},"priority":{"score":88.1,"factors":[{"name":"In a KEV catalog","points":35.0,"detail":"listed in CISA KEV and VulnCheck KEV"},{"name":"Recent KEV listing","points":0.0,"detail":"added 1947 days ago"},{"name":"Known ransomware use","points":10.0,"detail":"CISA KEV and VulnCheck KEV: Known"},{"name":"EPSS percentile","points":19.99,"detail":"percentile 0.9996"},{"name":"Named in threat reports","points":8.98,"detail":"4 reports"},{"name":"Public exploit code","points":5.0,"detail":"3 NVD references tagged Exploit; 28 PoC-in-GitHub repos; 1 Metasploit module"},{"name":"Mentioned in OTX pulses","points":3.0,"detail":"50 pulses"},{"name":"CVSS severity","points":6.16,"detail":"base score 8.8"},{"name":"End-of-life product","points":0.0,"detail":"supported or unknown"}]},"lineage":{"familyId":"fam-class-microsoft-windows-cwe-269"}}