CVE-2021-34523

Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2016 Cumulative Update 19, Microsoft Exchange Server 2016 Cumulative Update 20

Published 14 Jul 2021 · updated 10 Aug 2026 · Analyzed

9.0 Critical · CVSS 3.1, microsoft.com

Exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, with a remediation deadline of 17 Nov 2021 for US federal agencies. It has been used in ransomware campaigns.

Required action: Apply updates per vendor instructions.

Description

Microsoft Exchange Server Elevation of Privilege Vulnerability

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34523 · Patch, Vendor Advisory
packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html · Exploit, Third Party Advisory, VDB Entry
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34523 · Patch, Vendor Advisory
www.zerodayinitiative.com/advisories/ZDI-21-822/ · Third Party Advisory, VDB Entry
www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34523 · US Government Resource