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CVE-2026-45498 Microsoft CVE debrief

CVE-2026-45498 is a Microsoft Defender denial-of-service vulnerability that CISA added to its Known Exploited Vulnerabilities (KEV) catalog on 2026-05-20. Even though the CVSS score is 4.0 (Medium), KEV inclusion means organizations should treat it as a higher-priority remediation item because CISA has determined it is known to be exploited. The supplied corpus does not include affected versions, attack preconditions, or a public root-cause description, so the safest response is to follow Microsoft’s guidance and verify remediation on any Defender deployments in scope.

Vendor
Microsoft
Product
Defender
CVSS
MEDIUM 4
CISA KEV
Listed
Original CVE published
2026-05-20
Original CVE updated
2026-05-20
Advisory published
2026-05-20
Advisory updated
2026-05-20

Who should care

Security operations teams, endpoint security administrators, Microsoft Defender operators, vulnerability management owners, and IT teams responsible for Windows security tooling should prioritize this CVE. Organizations using Defender in production should verify whether they are affected and confirm remediation before the CISA due date.

Technical summary

The available source data identifies the issue as a denial-of-service vulnerability in Microsoft Defender. No further technical details are provided in the supplied corpus regarding the trigger, attack path, affected builds, or whether exploitation requires local access or special conditions. Because the vulnerability is listed in CISA’s KEV catalog, defenders should assume exploitation risk is credible and focus on vendor remediation guidance rather than waiting for additional public detail.

Defensive priority

High

Recommended defensive actions

  • Review the Microsoft Security Response Center guidance for CVE-2026-45498 and apply any available updates or mitigations.
  • Prioritize affected Microsoft Defender deployments for remediation before the CISA KEV due date of 2026-06-03.
  • Validate whether Microsoft Defender is used in cloud services or managed environments and follow applicable BOD 22-01 guidance if relevant.
  • If Microsoft indicates no mitigation is available for a deployment, consider CISA’s guidance to discontinue use of the product until a fix is available.
  • Monitor endpoint security health and alerting after remediation to confirm Defender service stability.

Evidence notes

This debrief is based only on the supplied CVE metadata and official references: CISA’s Known Exploited Vulnerabilities feed, the CVE record, and the NVD detail page. The corpus provides the vulnerability name, product, medium CVSS score, KEV status, and due date, but it does not include exploit mechanics, affected versions, or vendor remediation specifics beyond the linked Microsoft guidance reference in the CISA notes.

Official resources

CVE published and modified on 2026-05-20. CISA added the vulnerability to KEV on 2026-05-20 with a due date of 2026-06-03. This debrief does not use generation or review timestamps as the CVE issue date.