{"id":"CVE-2023-21529","kind":"vulnerability","aliases":["CVE-2023-21529"],"related":[],"title":"Microsoft Exchange Server Remote Code Execution Vulnerability","description":"Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.\n\nCISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","summary":"Microsoft Exchange Server has a deserialization flaw in which untrusted data is processed unsafely. An authenticated attacker can achieve remote code execution on the Exchange server.","severity":"high","cvss":8.8,"epss":null,"exploited":true,"exploited_at":"2026-04-13T00:00:00+00:00","products":[{"name":"Microsoft Exchange Server","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"microsoft exchange server","fixed":[],"affected":"= 2013","ecosystem":"vendor"},{"name":"microsoft exchange server","fixed":[],"affected":"= 2016","ecosystem":"vendor"},{"name":"microsoft exchange server","fixed":[],"affected":"= 2019","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exchange-server","exploited","on-prem-exchange","ransomware","vendor","windows"],"not_affected_if":["auth-required","exchange-online"],"how_to_check":null,"fix":"Apply the mitigations and patches per Microsoft's vendor instructions; the sources do not name specific versions or settings. If mitigations are unavailable, CISA says to discontinue use of the product.","status":"open","published_at":"2023-02-14T20:15:11+00:00","first_seen_at":"2026-10-23T19:11:51+00:00","triaged_at":"2026-10-23T20:38:56+00:00","updated_at":"2026-10-23T23:44:51+00:00","category":"vendor","confidence":0.6,"triage":{"at":"2026-10-23T20:38:56Z","model":"claude-haiku-5-5","output":{"fix":"Apply the mitigations and patches per Microsoft's vendor instructions; the sources do not name specific versions or settings. If mitigations are unavailable, CISA says to discontinue use of the product.","reach":"internet","summary":"Microsoft Exchange Server has a deserialization flaw in which untrusted data is processed unsafely. An authenticated attacker can achieve remote code execution on the Exchange server.","category":"vendor","who_cares":["exchange-server","on-prem-exchange","windows"],"confidence":0.6,"needs_auth":"yes","worst_case":"Attacker runs code on the Exchange server after authenticating.","analyst_note":"Find the Microsoft advisory for CVE-2023-21529 to get affected versions, the patch, and any mitigation steps, and check the KEV entry's ransomware tag.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["exchange-online","auth-required"],"user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000439,"input_tokens":2541,"output_tokens":370,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-01':94C '-2023':9A,12A '-21529':10A,13A '22':93C 'achiev':55B,78C 'action':84C 'allow':73C 'appli':85C 'applic':91C 'attack':53B,76C 'authent':52B,75C 'bod':92C 'cisa':82C 'cloud':97C 'code':5A,57B,80C 'contain':66C 'cve':8A,11A 'data':47B,71C 'deseri':42B,68C 'discontinu':100C 'exchang':2A,27B,33B,38B,61B,64C 'exchange':15A,18A,21A,24A 'exchange-serv':26B 'execut':6A,58B,81C 'exploit':29B 'flaw':43B 'follow':90C 'guidanc':95C 'instruct':89C 'microsoft':1A,14A,17A,20A,23A,37B,63C 'mitig':86C,106C 'on-prem-exchang':30B 'per':87C 'prem':32B 'process':49B 'product':104C 'ransomwar':34B 'remot':4A,56B,79C 'requir':83C 'server':3A,16A,19A,22A,25A,28B,39B,62B,65C 'servic':98C 'unavail':108C 'unsaf':50B 'untrust':46B,70C 'use':101C 'vendor':35B,88C 'vulner':7A 'window':36B","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2023-02-14T20:15:11+00:00","kev":{"dateAdded":"2026-04-13","dueDate":"2026-04-27","requiredAction":"Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","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-2023-21529","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2023-21529","severity":null,"published_at":"2026-04-13T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:51+00:00","fetched_at":"2026-10-25T16:39:45+00:00","note":null},{"source":"nvd","external_id":"CVE-2023-21529","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-21529","severity":null,"published_at":"2023-02-14T20:15:11+00:00","modified_at":"2026-08-19T17:18:05+00:00","first_seen_at":"2026-10-23T23:44:51+00:00","fetched_at":"2026-10-23T23:44:51+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"}