CVE-2026-45498: Microsoft Defender denial of service

CVE-2026-45498 · Severity: critical · CVSS 4 · Exploited in the wild · Published 2026-05-20

Microsoft Defender, the built-in antivirus and security suite for Windows, is susceptible to a denial of service vulnerability. An attacker could exploit this flaw to disable or crash the security software, potentially leaving the system unprotected against other threats. While the vulnerability is reported as being exploited in the wild, it requires local access to the target machine to execute.

Technologies: Microsoft Defender. Vendors: Microsoft.

Quick answers

Is CVE-2026-45498 exploited in the wild?
Yes. CVE-2026-45498 is known to be exploited in the wild, first recorded on 20 May 2026. Treat it as urgent.
How severe is CVE-2026-45498?
Critical severity, with a CVSS score of 4, published 20 May 2026.
Which products and versions are affected?
Microsoft Defender.
Is there a fix for CVE-2026-45498?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-45498 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-45498?
Check whether you run Microsoft Defender. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

Microsoft Defender is vulnerable to a denial of service (DoS) attack due to an unspecified flaw. The vulnerability is triggered via a local attack vector (AV:L) with low complexity and requires no special privileges or user interaction. Successful exploitation allows an attacker to impact the availability of the Defender service, potentially disabling real-time protection or scanning capabilities. Although the advisory mentions the flaw has been exploited in the wild, the CVSS score provided by Microsoft is 4.0 (Medium). Users should refer to the Microsoft Security Response Center (MSRC) for specific patch details and version information.

Affected products

  • Microsoft Defender

Timeline

  • 2026-05-20: disclosed
  • 2026-05-20: advisory
  • 2026-05-20: exploited: Reported as exploited in the wild in the advisory summary.

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