CVE-2021-31207
Published 2021-05-11 · Updated 2026-06-17 · Source secure@microsoft.com
Summary
CVE-2021-31207 is a medium-severity (CVSS 6.6) vulnerability in Microsoft Exchange Server. CISA added it to the Known Exploited Vulnerabilities catalog on November 3, 2021, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by November 17, 2021. CISA also lists it as known to be used in ransomware campaigns, so it should be prioritised accordingly. Microsoft has 390 vulnerabilities in the KEV catalog, 117 of them linked to ransomware.
All 390 known-exploited Microsoft vulnerabilities →Description
Microsoft Exchange Server Security Feature Bypass Vulnerability
CVSS vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
CISA Known-Exploited Vulnerability
Product: Microsoft — Exchange Server
Name: Microsoft Exchange Server Security Feature Bypass Vulnerability
Date added: 2021-11-03 · Due: 2021-11-17
Required action: Apply updates per vendor instructions.
References
- http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207
- https://www.zerodayinitiative.com/advisories/ZDI-21-819/
- http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207
- https://www.zerodayinitiative.com/advisories/ZDI-21-819/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207