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 0.917, as of
2026-09-16) - NVD CVSS v3.1
- 8.8 (HIGH)
- 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.
NVD description
Microsoft Exchange Server Remote Code Execution Vulnerability