CVE-2021-26858

Microsoft Exchange Server 2013 Cumulative Update 21, Microsoft Exchange Server 2013 Cumulative Update 22, Microsoft Exchange Server 2013 Cumulative Update 23

Published 3 Mar 2021 · updated 1 Oct 2026 · Analyzed

7.8 High · 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 3 May 2022 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-2021-26858 · Patch, Vendor Advisory
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858 · Patch, Vendor Advisory
www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858 · US Government Resource