CVE-2023-21529: Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability

Added to the CISA Known Exploited Vulnerabilities catalog on 13 Apr 2026. Vendor: Microsoft. Product: Exchange Server.

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. (due 27 Apr 2026)