{"id":"CVE-2021-26855","title":"Microsoft Exchange Server Remote Code Execution Vulnerability","summary":"Microsoft Exchange Server Remote Code Execution Vulnerability","severity":"critical","cvss":9.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","cwe":["CWE-918","CWE-918"],"vendor":"microsoft","product":"exchange_server","affected":["exchange_server = 2013","exchange_server = 2016","exchange_server = 2019"],"published":"2021-03-03","updated":"2026-08-12","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2021-26855","references":[{"url":"http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html","label":"secure@microsoft.com"},{"url":"http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html","label":"secure@microsoft.com"},{"url":"http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html","label":"secure@microsoft.com"},{"url":"http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html","label":"secure@microsoft.com"},{"url":"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855","label":"secure@microsoft.com"},{"url":"http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26855","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"tags":["nvd","kev","in-the-wild","exploit-available"],"epss":0.99996,"epssPercentile":0.99989,"kev":true,"kevDateAdded":"2021-11-03","kevDueDate":"2022-05-03","kevRansomware":true,"exploited":true,"exploitAvailable":true,"zeroDay":true,"ingestedAt":"2026-08-12T19:54:25.643Z","exploits":{"exploitdb":true,"github":51,"githubRepos":["https://github.com/sgnls/exchange-0days-202103","https://github.com/soteria-security/HAFNIUM-IOC","https://github.com/cert-lv/exchange_webshell_detection"],"metasploit":["auxiliary/gather/exchange_proxylogon_collector","auxiliary/scanner/http/exchange_proxylogon","exploit/windows/http/exchange_proxylogon_rce"],"nuclei":["CVE-2021-26855"],"checkedAt":"2026-09-19T16:22:51.230Z"},"slug":"CVE-2021-26855","body":"## Overview\n\nMicrosoft Exchange Server Remote Code Execution Vulnerability\n\n## Affected\n\n- `exchange_server = 2013`\n- `exchange_server = 2016`\n- `exchange_server = 2019`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"hadal","depthScore":100,"depthScoreParts":{"impact":50.1,"likelihood":20,"exploitation":25,"ransomware":5},"changes":[]}