{"id":"CVE-2021-31207","aliases":["EUVD-2021-18120","GHSA-jcxv-6f65-7hrx"],"status":"published","title":"Microsoft Exchange Server Security Feature Bypass Vulnerability","description":"Microsoft Exchange Server Security Feature Bypass Vulnerability","severity":{"version":"3.1","score":6.6,"vector":"CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.99782,"percentile":0.99955,"model":"v2026.06.15"},"facts":{"in_kev":true,"known_exploited":true,"public_exploit":true,"fix_available":false},"cwes":["CWE-20","CWE-22","CWE-434"],"published":"2021-05-11T19:11:41Z","modified":"2026-06-17T03:51:27Z","kev":{"date_added":"2021-11-03","due_date":"2021-11-17","required_action":"Apply updates per vendor instructions.","known_ransomware_use":"Known"},"exploitation":[{"source":"euvd","since":"2021-11-03"},{"source":"kev","since":"2021-11-03"}],"exploits":[{"source":"metasploit","id":"exploit/windows/http/exchange_proxyshell_rce","title":"Microsoft Exchange ProxyShell RCE","type":"exploit","platform":"Windows","date":"2021-04-06","verified":true,"url":"https://www.rapid7.com/db/modules/exploit/windows/http/exchange_proxyshell_rce"}],"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://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207","tags":["x_refsource_MISC","x_transferred","Patch","Vendor Advisory"]},{"url":"https://www.zerodayinitiative.com/advisories/ZDI-21-819/","tags":["x_refsource_MISC","x_transferred","Third Party Advisory","VDB Entry"]},{"url":"http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html","tags":["x_refsource_MISC","x_transferred","Exploit","Third Party Advisory","VDB Entry"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207","tags":["government-resource","US Government Resource"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-31207"},{"url":"https://www.zerodayinitiative.com/advisories/ZDI-21-819"},{"url":"https://github.com/advisories/GHSA-jcxv-6f65-7hrx"}],"sources":{"cve":[{"id":"CVE-2021-31207","title":"Microsoft Exchange Server Security Feature Bypass 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