CVE DATABASE / CVE-2021-31207
CVE-2021-31207
Microsoft Exchange Server Security Feature Bypass Vulnerability
CVSS 6.6 · MEDIUM
⚠ CISA KEV — ACTIVELY EXPLOITED
RANSOMWARE
On the CISA KEV catalog
Confirmed exploited in the wild. Added 2021-11-03.
Federal remediation due 2021-11-17.
Required action: Apply updates per vendor instructions.
Summary
Microsoft Exchange Server Security Feature Bypass Vulnerability
CVSS 3.1 breakdown
| Base score | 6.6 (MEDIUM) |
| Vector | CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H |
| Attack vector | NETWORK |
| Attack complexity | HIGH |
| Privileges required | HIGH |
| User interaction | NONE |
| Scope | UNCHANGED |
| Confidentiality | HIGH |
| Integrity | HIGH |
| Availability | HIGH |
Weakness type (CWE)
Affected products
Microsoft exchange server
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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/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207
Data: NIST NVD + CISA KEV. NVD last modified 2025-10-30. Always verify against the vendor advisory before acting.