CVE-2021-42321
KEVRansomware UseMicrosoft Exchange Server Remote Code Execution Vulnerability
Description
An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.
Microsoft Exchange Server Remote Code Execution Vulnerability
CVSS 3.1 vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HPublishedNov 10, 2021
Last modifiedAug 19, 2026
Added to KEVNov 17, 2021
Remediation dueDec 1, 2021
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321PatchVendor Advisory
- packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.htmlExploitThird Party Advisory
- packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.htmlExploitThird Party Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321PatchVendor Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321US Government Resource
0 recent articles mention this CVE
93
Risk assessment · Critical
Actively exploited and used by ransomware crews. Patch immediately.
- Exploitation
- Confirmed in the wild (CISA KEV)
- Federal remediation deadline
- Overdue by 1791 days
- Ransomware
- Used in known ransomware campaigns
- CVSS
- 8.8 HIGH
- EPSS (30-day exploit probability)
- 91.7% · top 1% of all CVEs
- Weakness
- NVD-CWE-Other
- Attack vector
- Network, remotely reachable
Recommended actions
- 1.Apply updates per vendor instructions.
- 2.Treat as emergency change: patch or isolate internet-facing instances first.
- 3.Review exposure: confirm which instances are reachable from the internet and restrict access until patched.
- 4.Hunt for compromise: review logs for the disclosure window, not just from the patch date.
- 5.Verify offline/immutable backups and segment the affected systems. This flaw is used for ransomware initial access.
Assessment is derived automatically from the live signals above; verify against your own asset inventory.