{"id":"CVE-2021-33766","aliases":["EUVD-2021-20443","GHSA-f9f4-96j3-5mvr"],"status":"published","title":"Microsoft Exchange Server Information Disclosure Vulnerability","description":"Microsoft Exchange Server Information Disclosure Vulnerability","severity":{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.98176,"percentile":0.99914,"model":"v2026.06.15"},"facts":{"in_kev":true,"known_exploited":true,"public_exploit":true,"fix_available":false},"cwes":["CWE-287"],"published":"2021-07-14T17:53:40Z","modified":"2026-08-10T19:58:44Z","kev":{"date_added":"2022-01-18","due_date":"2022-02-01","required_action":"Apply updates per vendor instructions.","known_ransomware_use":"Unknown"},"exploitation":[{"source":"euvd","since":"2022-01-18"},{"source":"kev","since":"2022-01-18"}],"exploits":[{"source":"pocgithub","id":"bhdresh/CVE-2021-33766","title":"bhdresh/CVE-2021-33766","date":"2021-08-31","url":"https://github.com/bhdresh/CVE-2021-33766"},{"source":"pocgithub","id":"demossl/CVE-2021-33766-ProxyToken","title":"demossl/CVE-2021-33766-ProxyToken","date":"2021-09-15","url":"https://github.com/demossl/CVE-2021-33766-ProxyToken"},{"source":"nuclei","id":"CVE-2021-33766","title":"Microsoft Exchange - Authentication Bypass","type":"detection template","url":"https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-33766.yaml"}],"products":[{"vendor":"microsoft","product":"exchange server"},{"vendor":"microsoft","product":"exchange_server"},{"vendor":"microsoft","product":"microsoft exchange server 2013 cumulative update 23"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 19"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 20"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 8"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 9"}],"references":[{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766","tags":["vendor-advisory","patch","Patch","Vendor Advisory"]},{"url":"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766","tags":["x_refsource_MISC","x_transferred","Patch","Vendor Advisory"]},{"url":"https://www.zerodayinitiative.com/advisories/ZDI-21-798/","tags":["x_refsource_MISC","x_transferred","Third Party Advisory","VDB Entry"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766","tags":["government-resource","US Government Resource"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-33766"},{"url":"https://www.zerodayinitiative.com/advisories/ZDI-21-798"},{"url":"https://github.com/advisories/GHSA-f9f4-96j3-5mvr"}],"sources":{"cve":[{"id":"CVE-2021-33766","title":"Microsoft Exchange Server Information Disclosure Vulnerability","description":"Microsoft Exchange Server Information Disclosure Vulnerability","status":"published","published":"2021-07-14T17:53:40Z","modified":"2026-08-10T15:11:36.358Z","cvss":[{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C","level":"high","assessor":"cna"}],"updated_at":"2026-11-02T14:33:10.204494Z"}],"euvd":[{"id":"EUVD-2021-20443","description":"Microsoft Exchange Server Information Disclosure Vulnerability","status":"published","published":"2021-07-14T17:53:40Z","modified":"2026-08-10T15:11:36Z","cvss":[{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C","level":"high"}],"exploited_since":"2022-01-18","updated_at":"2026-11-02T18:02:04.178454Z"}],"ghsa":[{"id":"GHSA-f9f4-96j3-5mvr","title":"Microsoft Exchange Information Disclosure Vulnerability","description":"Microsoft Exchange Information Disclosure Vulnerability","status":"published","published":"2022-05-24T19:07:54Z","modified":"2026-08-10T18:31:37Z","cvss":[{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"high"}],"cwes":["CWE-287"],"updated_at":"2026-11-02T15:10:15.270288Z"}],"kev":[{"id":"CVE-2021-33766","title":"Microsoft Exchange Server Information Disclosure","description":"Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.","cwes":["CWE-287"],"kev":{"date_added":"2022-01-18","due_date":"2022-02-01","required_action":"Apply updates per vendor instructions.","known_ransomware_use":"Unknown"},"updated_at":"2026-11-02T17:00:16.541131Z"}],"nvd":[{"id":"CVE-2021-33766","description":"Microsoft Exchange Server Information Disclosure Vulnerability","status":"published","published":"2021-07-14T18:15:10.38Z","modified":"2026-08-10T19:58:44.54Z","cvss":[{"version":"3.1","score":7.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"high","assessor":"secondary"},{"version":"2.0","score":5,"vector":"AV:N/AC:L/Au:N/C:P/I:N/A:N","level":"medium","assessor":"primary"}],"updated_at":"2026-11-02T14:06:55.747384Z"}]}}