CVE-2021-42321

Microsoft Exchange Server 2016 Cumulative Update 21, Microsoft Exchange Server 2016 Cumulative Update 22, Microsoft Exchange Server 2019 Cumulative Update 10

Published 10 Nov 2021 · updated 19 Aug 2026 · Analyzed

8.8 High · CVSS 3.1, microsoft.com

Exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on 17 Nov 2021, with a remediation deadline of 1 Dec 2021 for US federal agencies. It has been used in ransomware campaigns.

Required action: Apply updates per vendor instructions.

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321 · Patch, Vendor Advisory
packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html · Exploit, Third Party Advisory, VDB Entry
packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html · Exploit, Third Party Advisory, VDB Entry
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321 · Patch, Vendor Advisory
www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321 · US Government Resource