CVE-2023-21529 — Microsoft Exchange Server: Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
CVE-2023-21529 — Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
What This Means For You
- CISA has confirmed active exploitation — immediate patching required.
- Added to CISA KEV catalog — federal agencies must remediate by 2026-04-27.
Related ATT&CK Techniques
🛡️ Detection Rules
5 rules · 5 SIEM formats5 auto-generated detection rules for this incident, mapped to MITRE ATT&CK. Available in Sigma, Splunk SPL, Sentinel KQL, Elastic Lucene, and QRadar AQL.
Web Application Exploitation Attempt — CVE-2023-21529
Get this rule in your SIEM's native format — copy, paste, detect. No manual conversion.
5 Sigma rules mapped to the ATT&CK techniques from this breach — pick your SIEM and get a ready-to-paste query.
Get Detection Rules →Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2023-21529 | RCE | Microsoft Exchange Server |
| CVE-2023-21529 | Deserialization | Deserialization of untrusted data |
Source & Attribution
| Source Platform | CISA |
| Channel | CISA KEV |
| Published | April 13, 2026 at 15:00 UTC |
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