VulnerabilityAnalyzed
CVE-2023-21529
Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
KEVHIGH 8.8EPSS 62.1%
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 27 April 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
- CVSS 3.1
- 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 62.10% probability · 99th percentile
- CISA KEV
- Listed 13 April 2026 · due 27 April 2026 · used in ransomware campaigns
- Weakness
- CWE-502
- Affected
- microsoft/exchange server
- Source
- secure@microsoft.com
CISA notes
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529 ; https://nvd.nist.gov/vuln/detail/CVE-2023-21529
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529Patch, Vendor Advisory
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529Patch, Vendor Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21529US Government Resource
- https://www.microsoft.com/en-us/security/blog/2026/04/06/storm-1175-focuses-gaze-on-vulnerable-web-facing-assets-in-high-tempo-medusa-ransomware-operations/Technical Description
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.