November 17, 2021 · Applied Cybernetics Group
CVE-2021-42321 — Microsoft Exchange
known ransomware use
Microsoft Exchange Server Remote Code Execution Vulnerability
- Added to KEV
2021-11-17- Federal due date
2021-12-01- Vendor
- Microsoft
- Product
- Exchange
- EPSS
- 99.8th percentile (score 0.904, as of
2026-07-13) - NVD CVSS v3.1
- —
- Ransomware use
- Known
- ATT&CK
- T1059 , T1078 · signal rollup
- Upstream
- https://nvd.nist.gov/vuln/detail/CVE-2021-42321
CISA short description
An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.
Required action
Apply updates per vendor instructions.