{"id":"CVE-2021-34523","kind":"vulnerability","aliases":["CVE-2021-34523"],"related":[],"title":"Microsoft Exchange Server: Microsoft Exchange Server Privilege Escalation Vulnerability","description":"Microsoft Exchange Server contains an unspecified vulnerability that allows for privilege escalation.\n\nCISA required action: Apply updates per vendor instructions.","summary":"Microsoft Exchange Server has a privilege escalation flaw that CISA lists as actively exploited, with ransomware use noted in its catalog entry. An attacker who gets a foothold can gain higher privileges on the Exchange server.","severity":"critical","cvss":9.8,"epss":0.9999,"exploited":true,"exploited_at":"2021-11-03T00:00:00+00:00","products":[{"name":"Microsoft Exchange Server","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exchange-server","exploited","infrastructure","on-prem-email","ransomware","windows"],"not_affected_if":["exchange-online","microsoft-365-cloud-only"],"how_to_check":null,"fix":"Apply the Microsoft updates for Exchange Server per vendor instructions, as CISA requires; the specific patch version is unknown from these sources.","status":"open","published_at":"2021-07-14T18:15:12+00:00","first_seen_at":"2026-10-23T19:11:53+00:00","triaged_at":"2026-10-23T21:39:31+00:00","updated_at":"2026-10-23T21:57:35+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-23T21:39:31Z","model":"claude-haiku-5-5","output":{"fix":"Apply the Microsoft updates for Exchange Server per vendor instructions, as CISA requires; the specific patch version is unknown from these sources.","reach":"unknown","impact":"high","summary":"Microsoft Exchange Server has a privilege escalation flaw that CISA lists as actively exploited, with ransomware use noted in its catalog entry. An attacker who gets a foothold can gain higher privileges on the Exchange server.","category":"infrastructure","who_cares":["exchange-server","windows","on-prem-email"],"confidence":0.6,"needs_auth":"unknown","worst_case":"Attacker escalates privileges on the Exchange server, possibly to full control","analyst_note":"Find the Microsoft advisory for CVE-2021-34523 and the affected and fixed Exchange builds, plus how to detect exploitation, since the sources give none of these.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["exchange-online","microsoft-365-cloud-only"],"user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000478,"input_tokens":2826,"output_tokens":391,"severity_before":"unknown"},"analyst_status":"queued","analyst_note":"Find the Microsoft advisory for CVE-2021-34523 and the affected and fixed Exchange builds, plus how to detect exploitation, since the sources give none of these.","search":"'-2021':11A,14A '-34523':12A,15A 'action':80C 'activ':42B 'allow':74C 'appli':81C 'attack':53B 'catalog':50B 'cisa':39B,78C 'contain':69C 'cve':10A,13A 'email':27B 'entri':51B 'escal':8A,36B,77C 'exchang':2A,5A,20B,31B,64B,67C 'exchange':17A 'exchange-serv':19B 'exploit':22B,43B 'flaw':37B 'foothold':57B 'gain':59B 'get':55B 'higher':60B 'infrastructur':23B 'instruct':85C 'list':40B 'microsoft':1A,4A,16A,30B,66C 'note':47B 'on-prem-email':24B 'per':83C 'prem':26B 'privileg':7A,35B,61B,76C 'ransomwar':28B,45B 'requir':79C 'server':3A,6A,18A,21B,32B,65B,68C 'unspecifi':71C 'updat':82C 'use':46B 'vendor':84C 'vulner':9A,72C 'window':29B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2021-07-14T18:15:12+00:00","kev":{"dateAdded":"2021-11-03","dueDate":"2021-11-17","requiredAction":"Apply updates per vendor instructions.","knownRansomwareCampaignUse":"Known"},"cvss_vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N","cvss_by":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2021-34523","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-34523","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":"2026-10-25T16:39:50+00:00","note":null},{"source":"epss","external_id":"CVE-2021-34523","url":"https://api.first.org/data/v1/epss?cve=CVE-2021-34523","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-2021-34523","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-34523","severity":null,"published_at":"2021-07-14T18:15:12+00:00","modified_at":"2026-08-10T19:59:11+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"}