CVE DATABASE / CVE-2021-42321
CVE-2021-42321
Microsoft Exchange Server Remote Code Execution Vulnerability
CVSS 8.8 · HIGH
⚠ CISA KEV — ACTIVELY EXPLOITED
RANSOMWARE
On the CISA KEV catalog
Confirmed exploited in the wild. Added 2021-11-17.
Federal remediation due 2021-12-01.
Required action: Apply updates per vendor instructions.
Summary
Microsoft Exchange Server Remote Code Execution Vulnerability
CVSS 3.1 breakdown
| Base score | 8.8 (HIGH) |
| Vector | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
| Attack vector | NETWORK |
| Attack complexity | LOW |
| Privileges required | LOW |
| User interaction | NONE |
| Scope | UNCHANGED |
| Confidentiality | HIGH |
| Integrity | HIGH |
| Availability | HIGH |
Affected products
Microsoft exchange server
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References
- http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html
- http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321
Data: NIST NVD + CISA KEV. NVD last modified 2025-10-30. Always verify against the vendor advisory before acting.