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CISA KEV Alert — Active Real-World Exploitation Confirmed
This vulnerability is in the CISA Known Exploited Vulnerabilities catalog and is being actively exploited right now.
Microsoft Defender Denial of Service Vulnerability (CVE-2026-45498) | MSSP Advisory
High🔴 KEV ALERTConfirmed
DateMay 20, 2026
CVECVE-2026-45498
📋Executive Summary
CISA added CVE-2026-45498 to the Known Exploited Vulnerabilities catalog, flagging an unspecified Microsoft Defender denial of service vulnerability. MSSPs face immediate exposure through their own security stack and must advise clients on Defender deployments across their environments.
⚠️Why It Matters for MSSPs
Your RMM and endpoint security monitoring depends on Defender functioning properly, and a DoS attack could blind your security operations. Every client running Defender becomes a potential blind spot in your monitoring capability, creating liability if incidents occur during service disruption.
✅Recommended Action
Audit all client Defender deployments within 24 hours and apply Microsoft's mitigation guidance immediately. Contact clients with Defender installations to communicate the risk and document your advisory in writing for liability protection.
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🏷️Threat Category
Vulnerability Disclosure
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