{"id":"CVE-2021-26858","aliases":["EUVD-2021-13642","GHSA-r4wp-245q-vr5w"],"status":"published","title":"Microsoft Exchange Server Remote Code Execution Vulnerability","description":"Microsoft Exchange Server Remote Code Execution Vulnerability","severity":{"version":"3.1","score":7.8,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.93651,"percentile":0.99844,"model":"v2026.06.15"},"facts":{"in_kev":true,"known_exploited":true,"public_exploit":false,"fix_available":false},"published":"2021-03-02T23:55:27Z","modified":"2026-10-01T21:17:16Z","kev":{"date_added":"2021-11-03","due_date":"2022-05-03","required_action":"Apply updates per vendor instructions.","known_ransomware_use":"Known"},"exploitation":[{"source":"euvd","since":"2021-11-03"},{"source":"kev","since":"2021-11-03"}],"products":[{"vendor":"microsoft","product":"exchange server"},{"vendor":"microsoft","product":"exchange_server"},{"vendor":"microsoft","product":"microsoft exchange server 2013 cumulative update 21"},{"vendor":"microsoft","product":"microsoft exchange server 2013 cumulative update 22"},{"vendor":"microsoft","product":"microsoft exchange server 2013 cumulative update 23"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 10"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 11"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 12"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 13"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 14"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 15"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 16"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 17"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 18"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 19"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 8"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 9"},{"vendor":"microsoft","product":"microsoft exchange server 2019"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 1"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 2"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 3"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 4"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 5"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 6"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 7"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 8"}],"references":[{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858","tags":["vendor-advisory","patch","Patch","Vendor Advisory"]},{"url":"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858","tags":["x_refsource_MISC","x_transferred","Patch","Vendor Advisory"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858","tags":["government-resource","US Government Resource"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-26858"},{"url":"https://github.com/advisories/GHSA-r4wp-245q-vr5w"}],"sources":{"cve":[{"id":"CVE-2021-26858","title":"Microsoft Exchange Server Remote Code Execution Vulnerability","description":"Microsoft Exchange Server Remote Code Execution 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CVE-2021-26857, CVE-2021-27065, CVE-2021-27078.","status":"published","published":"2022-05-24T17:43:35Z","modified":"2026-08-19T18:32:32Z","cvss":[{"version":"3.1","score":7.8,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:10:42.300371Z"}],"kev":[{"id":"CVE-2021-26858","title":"Microsoft Exchange Server Remote Code Execution Vulnerability","description":"Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.","kev":{"date_added":"2021-11-03","due_date":"2022-05-03","required_action":"Apply updates per vendor instructions.","known_ransomware_use":"Known"},"updated_at":"2026-11-02T17:00:17.050017Z"}],"nvd":[{"id":"CVE-2021-26858","description":"Microsoft Exchange Server Remote Code Execution Vulnerability","status":"published","published":"2021-03-03T00:15:12.227Z","modified":"2026-10-01T21:17:16.777Z","cvss":[{"version":"3.1","score":7.8,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high","assessor":"secondary"},{"version":"3.1","score":7.8,"vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high","assessor":"secondary"},{"version":"2.0","score":6.8,"vector":"AV:N/AC:M/Au:N/C:P/I:P/A:P","level":"medium","assessor":"primary"}],"updated_at":"2026-11-02T14:06:50.399901Z"}]}}