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Microsoft Defender Zero-Days Under Active Attack!
23 May
Summary
- Microsoft patches two actively exploited zero-day flaws in Defender.
- Flaws allow privilege escalation and denial of service attacks.
- CISA added vulnerabilities to its KEV catalog with a June 3 deadline.
Microsoft has released critical security updates to address two zero-day vulnerabilities that were actively exploited in its Defender antivirus product. The first, tracked as CVE-2026-41091, is a privilege escalation flaw with a high severity score, while the second, CVE-2026-45498, is a denial-of-service vulnerability, also rated as high severity.
These vulnerabilities were fixed via automatic updates to the Malware Protection Engine (version 1.1.26040.8) and the Antimalware Platform (version 4.18.26040.7). Although updates are typically automatic, users are advised to verify their versions. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has included both bugs in its Known Exploited Vulnerabilities (KEV) catalog.
As a result, federal agencies must apply the patches or discontinue use of vulnerable software by June 3, 2026. CISA highlighted that such vulnerabilities pose significant risks and are a frequent attack vector for malicious cyber actors.
