CVE-2023-21529

Microsoft Exchange Server Remote Code Execution Vulnerability

CVE-2023-21529 is fixed in 4 products on 1 platform, first by KB5023038, released February 14, 2023. It is being exploited: CISA added it to the Known Exploited Vulnerabilities catalog on April 13, 2026, with known ransomware use. Patch Radar priority: Patch now.

Patch nowCISA KEVKnown ransomware use

CVSS

8.8

Important

Exploitation

Exploited

Listed by CISA

CISA KEV

Apr 13, 2026

Federal due date Apr 27, 2026. Known ransomware use

EPSS

0.5929

99th percentile

Where it's fixed

Product	Fix	Released
Microsoft
Microsoft Exchange Server 2013 Cumulative Update 23	KB5023038	Feb 14, 2023
Microsoft Exchange Server 2016 Cumulative Update 23	KB5023038	Feb 14, 2023
Microsoft Exchange Server 2019 Cumulative Update 11	KB5023038	Feb 14, 2023
Microsoft Exchange Server 2019 Cumulative Update 12	KB5023038	Feb 14, 2023

Details

Published
February 14, 2023
Weakness
Deserialization of Untrusted Data
CISA required action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529

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