CVE-2026-45498
Microsoft Defender Denial of Service Vulnerability
Microsoft Defender
Microsoft Defender Denial of Service Vulnerability
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 20 May 2026. US federal agencies were required to remediate it by 3 June 2026.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 1.3%, which is higher than 69.6% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Frequently asked questions
Is CVE-2026-45498 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2026-45498.
What does CVE-2026-45498 affect?
CVE-2026-45498 affects Microsoft Defender. Microsoft Defender Denial of Service Vulnerability
How severe is CVE-2026-45498?
CVE-2026-45498 is rated MEDIUM with a CVSS base score of 4. EPSS puts the probability of exploitation in the next 30 days at 1.3%, higher than 69.6% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 3 June 2026.
How should organisations respond to CVE-2026-45498?
Apply the vendor patch for Microsoft Defender as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.