{"schemaVersion":3,"id":"CVE-2021-42321","aliases":[],"status":"published","duplicateOf":null,"title":"Microsoft Exchange Server Remote Code Execution Vulnerability","description":"Microsoft Exchange Server Remote Code Execution Vulnerability","dates":{"published":"2021-11-10T00:47:43.000Z","modified":"2026-08-19T16:27:07.165Z","reserved":null,"kevAdded":["2021-11-17T00:00:00.000Z"],"kevDue":["2021-12-01T00:00:00.000Z"]},"cvss":{"headline":{"score":8.8,"severity":"high","version":"3.1","versionLabel":"v3.1","source":"CVE.org","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C","computed":false,"selection":"backend-summary"},"metrics":[{"version":"3.1","versionLabel":"v3.1","source":"CVE.org","score":8.8,"severity":"high","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C","exploitability":null,"impact":null,"computed":false},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":8.8,"severity":"high","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","exploitability":null,"impact":null,"computed":false},{"version":"2.0","versionLabel":"v2.0","source":"NVD","score":6.5,"severity":"medium","vector":"AV:N/AC:L/Au:S/C:P/I:P/A:P","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.91737,"percentile":0.99817,"severity":"critical","asOf":"2026-10-20T00:00:00.000Z","change":{"pp":0,"baselineDate":"2026-09-20T00:00:00.000Z","baselineScore":0.91737},"history":[{"date":"2026-09-14T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-15T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-16T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-17T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-18T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-19T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-20T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.91737,"percentile":0.99817}],"last30":[{"date":"2026-09-20T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.91737,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.91737,"percentile":0.99817}]},"kev":{"state":"listed","entries":[{"source":"cisa","sourceLabel":"CISA","dateAdded":"2021-11-17T00:00:00.000Z","dueDate":"2021-12-01T00:00:00.000Z","requiredAction":"Apply updates per vendor instructions.","name":"Microsoft Exchange Server Remote Code Execution Vulnerability","description":"An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.","notes":[{"type":"url","href":"https://nvd.nist.gov/vuln/detail/CVE-2021-42321","label":"nvd.nist.gov/vuln/detail/CVE-2021-42321"}],"vendor":"Microsoft","product":"Exchange","ransomware":true,"ransomwareUse":"Known","exploitationType":null}],"listedCount":1,"totalCatalogs":3,"catalogs":[{"source":"cisa","label":"CISA","listed":true,"entry":{"source":"cisa","sourceLabel":"CISA","dateAdded":"2021-11-17T00:00:00.000Z","dueDate":"2021-12-01T00:00:00.000Z","requiredAction":"Apply updates per vendor instructions.","name":"Microsoft Exchange Server Remote Code Execution Vulnerability","description":"An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.","notes":[{"type":"url","href":"https://nvd.nist.gov/vuln/detail/CVE-2021-42321","label":"nvd.nist.gov/vuln/detail/CVE-2021-42321"}],"vendor":"Microsoft","product":"Exchange","ransomware":true,"ransomwareUse":"Known","exploitationType":null}},{"source":"enisa","label":"ENISA","listed":false,"entry":null},{"source":"circl","label":"CIRCL","listed":false,"entry":null}]},"ransomware":{"state":"known","sources":["cisa"]},"exploits":[{"id":"REF_068852C88B0BC0D3","name":"Exploit Reference (packetstormsecurity.com)","source":"reference","url":"http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html","maturity":"unknown","reliabilityScore":0.2,"verified":false,"type":null,"platforms":[],"requiresAuth":null,"exploitdb":null,"metasploit":null},{"id":"REF_C046F92753CCA14D","name":"Exploit Reference (packetstormsecurity.com)","source":"reference","url":"http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html","maturity":"unknown","reliabilityScore":0.2,"verified":false,"type":null,"platforms":[],"requiresAuth":null,"exploitdb":null,"metasploit":null},{"id":"MSF_EXPLOIT_WINDOWS_HTTP_EXCHANGE_CHAINEDSERIALIZATIONBINDER_RCE","name":"Microsoft Exchange Server ChainedSerializationBinder RCE","source":"metasploit","url":"https://github.com/rapid7/metasploit-framework/blob/master/modules/exploit/windows/http/exchange_chainedserializationbinder_rce.rb","maturity":"weaponized","reliabilityScore":1,"verified":true,"type":"remote","platforms":[],"requiresAuth":true,"exploitdb":null,"metasploit":{"fullname":"exploit/windows/http/exchange_chainedserializationbinder_rce","rank":"600","rankName":"excellent","postAuth":true,"check":true,"stability":["crash-safe"],"sideEffects":["ioc-in-logs","config-changes"],"reliability":["repeatable-session"]}}],"exploitCount":3,"weaknesses":[],"affected":[{"vendor":"microsoft","product":"exchange_server","name":"Exchange Server","label":"exchange_server","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"2016:cumulative_update_21","noFixRecorded":false,"fixedIn":null},{"text":"2016:cumulative_update_22","noFixRecorded":false,"fixedIn":null},{"text":"2019:cumulative_update_10","noFixRecorded":false,"fixedIn":null},{"text":"2019:cumulative_update_11","noFixRecorded":false,"fixedIn":null}],"versionsText":"2016:cumulative_update_21 | 2016:cumulative_update_22 | 2019:cumulative_update_10 | 2019:cumulative_update_11","eol":{"isEol":null,"eolDate":null,"matchMethod":"cpe","cycle":null,"product":{"name":"msexchange","label":"Microsoft Exchange","category":"server-app"}},"hubHref":"/vendor/microsoft/exchange_server"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 21","name":"Microsoft Exchange Server 2016 Cumulative Update 21","label":"microsoft exchange server 2016 cumulative update 21","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≥ 15.01.0, < 15.01.2308.020","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 15.01.0, < 15.01.2308.020","eol":null,"hubHref":"/vendor/microsoft/microsoft_exchange_server_2016_cumulative_update_21"},{"vendor":"microsoft","product":"microsoft exchange server 2016 cumulative update 22","name":"Microsoft Exchange Server 2016 Cumulative Update 22","label":"microsoft exchange server 2016 cumulative update 22","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≥ 15.0.0, < 15.01.2375.017","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 15.0.0, < 15.01.2375.017","eol":null,"hubHref":"/vendor/microsoft/microsoft_exchange_server_2016_cumulative_update_22"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 10","name":"Microsoft Exchange Server 2019 Cumulative Update 10","label":"microsoft exchange server 2019 cumulative update 10","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≥ 15.02.0, < 15.02.0792.019","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 15.02.0, < 15.02.0792.019","eol":null,"hubHref":"/vendor/microsoft/microsoft_exchange_server_2019_cumulative_update_10"},{"vendor":"microsoft","product":"microsoft exchange server 2019 cumulative update 11","name":"Microsoft Exchange Server 2019 Cumulative Update 11","label":"microsoft exchange server 2019 cumulative update 11","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≥ 15.02.0, < 15.02.0986.014","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 15.02.0, < 15.02.0986.014","eol":null,"hubHref":"/vendor/microsoft/microsoft_exchange_server_2019_cumulative_update_11"}],"affectedCount":5,"eol":{"hasEol":false,"count":0},"references":[{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321","label":"msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321","hostname":"msrc.microsoft.com","tags":["Vendor Advisory","Patch"]},{"url":"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321","label":"portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321","hostname":"portal.msrc.microsoft.com","tags":["X Refsource MISC","X Transferred","Patch","Vendor Advisory"]},{"url":"http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html","label":"packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html","hostname":"packetstormsecurity.com","tags":["X Refsource MISC","X Transferred","Exploit","Third Party Advisory","VDB Entry"]},{"url":"http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html","label":"packetstormsecurity.com/files/…","hostname":"packetstormsecurity.com","tags":["X Refsource MISC","X Transferred","Exploit","Third Party Advisory","VDB Entry"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321","label":"www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321","hostname":"www.cisa.gov","tags":["Government Resource","US Government Resource"]}],"lineage":{"upstream":[],"downstream":[],"duplicates":[],"related":[]},"timeline":[{"kind":"published","date":"2021-11-10T00:47:43.000Z","label":"Published","detail":"Vulnerability first disclosed.","source":null},{"kind":"kev-added","date":"2021-11-17T00:00:00.000Z","label":"Added to CISA KEV","detail":"Microsoft Exchange Server Remote Code Execution Vulnerability","source":"cisa"},{"kind":"kev-due","date":"2021-12-01T00:00:00.000Z","label":"CISA remediation due","detail":"Apply updates per vendor instructions.","source":"cisa"},{"kind":"modified","date":"2026-08-19T16:27:07.165Z","label":"Last modified","detail":"Vulnerability information updated.","source":null}],"risk":{"score":90,"level":"critical","profile":"Default","thresholds":{"critical":75,"high":50,"medium":25,"low":10}},"meta":{"dataAsOf":"2026-10-21T03:34:33.971Z","stale":false,"partial":false}}