Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
Microsoft · Exchange Server
CVSS 8.8
EPSS 62%
no public exploit indexed
ransomware
Fix deadline passed 27 April 2026
What it is
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
Why we say that
- Linked by CISA to known ransomware campaigns
- EPSS puts exploitation in the next 30 days at 62%
- CISA's federal remediation deadline (2026-04-27) has passed
- Listed in the CISA Known Exploited Vulnerabilities catalogue
Every line above comes from a named public source. Where the evidence is thin, we say so rather than inventing confidence — see methodology.
What to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
What it costs when this goes wrong
This is where UK enforcement meets the vulnerability record. This vulnerability is used in ransomware campaigns; here is what ransomware has cost UK organisations at the regulator.
- Advanced Computer Software Group Limited The Information Commissioner’s Office (ICO) has fined Advanced Computer Software Group Ltd (Advanced) £3.07m for security failings…
- Optionis Group Limited The data controller suffered a ransomware attack, which resulted in the exfiltration of personal data. A reprimand was issued in r…