What’s Vulnerable › Vulnerabilities

CVE-2021-31978: Microsoft Defender Denial of Service Vulnerability

• Severity: low (CVSS 2.1 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-06-08 · updated 2026-06-17

Description

Microsoft Defender Denial of Service Vulnerability

Affected products

• Microsoft Malware Protection Engine: before 1.1.18200.3 — fixed in 1.1.18200.3
• Microsoft Malware Protection Engine: from 1.1.0.0 before Version 1.1.18200.3 — fixed in Version 1.1.18200.3

How to fix

Upgrade to a fixed version: Microsoft Malware Protection Engine 1.1.18200.3; Microsoft Malware Protection Engine Version 1.1.18200.3. Check the vendor advisory for mitigations.

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31978
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31978

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