CVE-2023-21529 Known ransomware use

Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability

Microsoft — Exchange Server

Added to KEV catalog: 13 April 2026
Federal remediation due date: 27 April 2026
Weakness classification (CWE): CWE-502

CISA Description

Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.

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.

Notes

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529 ; https://nvd.nist.gov/vuln/detail/CVE-2023-21529

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