CVE-2023-21529VulnerabilityPublished 04/13/2026Updated 10/24/2026
CVE-2023-21529: Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
Affects Microsoft Exchange ServerSource CISA KEV
Severity
HighNo CVSS score published yet
- Exploitation
Actively exploited – in CISA KEV since 04/13/2026
- KEV deadline
- 04/27/2026
- Ransomware
- Used in ransomware campaigns
- EPSS
- 59.3% chance of exploitation in 30 days – higher than 99% of CVEs
What to do
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.
Description
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.