Denial of Service Vulnerability in Microsoft Defender by Microsoft
CVE-2026-45498

4MEDIUM

Key Information:

Vendor

Microsoft
Status
Microsoft Defender Antimalware Platform
Vendor
CVE Published:
20 May 2026

Badges

👾 Exploit Exists🦅 CISA Reported📰 News Worthy

What is CVE-2026-45498?

A vulnerability in Microsoft Defender allows attackers to cause a denial of service. An unauthenticated user may exploit this issue to disrupt service functionality, potentially leading to operational interruptions. It is crucial for users of Microsoft Defender to apply relevant patches and updates to mitigate the risk associated with this vulnerability.

CISA has reported CVE-2026-45498

CISA provides regional cyber and physical services to support security and resilience across the United States. CISA monitor the most dangerious vulnerabilities and have identifed CVE-2026-45498 as being exploited but is not known by the CISA to be used in ransomware campaigns. This is subject to change at pace

The CISA's recommendation is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Affected Version(s)

Microsoft Defender Antimalware Platform 4.0.0.0 < 4.18.26040.7

News Articles

favicon imageTechtimes

Microsoft Defender Zero-Days Patched: RedSun, UnDefend Exploits Already Used in Live Intrusions

Microsoft pushed out-of-band patches on May 21, 2026, for two actively exploited Windows Defender zero-days — one that lets a low-privileged attacker seize full SYSTEM-level control of any Windows

3 weeks ago

favicon imageForbes

2 New Microsoft Defender Zero-Days Exploited—Patch Now Rolling Out

Microsoft has confirmed an emergency security update as CISA warns that two new Defender zero-days are being exploited by attackers.

3 weeks ago

favicon imageOnmsft

Microsoft Patches Two Actively Exploited Defender Zero-Days on Windows

Microsoft patched two actively exploited Defender zero-days affecting Windows systems and security components.

3 weeks ago

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE...
vendor-advisorypatch

CVSS V3.1

Score:
4
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Local
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • đź“°

    First article discovered by Help Net Security

  • đź‘ľ

    Exploit known to exist

  • 🦅

    CISA Reported

  • Vulnerability published

  • Vulnerability Reserved

.