How severe is CVE-2021-31978?

CVE-2021-31978 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-31978 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31978?

CVE-2021-31978 affects Microsoft Malware Protection Engine. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-31978?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-31978 published?

CVE-2021-31978 was published on 2021-06-08 and last updated on 2026-06-17.

CVE-2021-31978

CVE-2021-31978 is a medium-severity vulnerability in Microsoft Malware Protection Engine with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
CVSS v2: 2.1
EPSS exploit prediction: 1% (65th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Microsoft Malware Protection Engine
Published: 2021-06-08
Last modified: 2026-06-17

Description

Microsoft Defender Denial of Service Vulnerability

Frequently asked questions

What is CVE-2021-31978?: Microsoft Defender Denial of Service Vulnerability
How severe is CVE-2021-31978?: CVE-2021-31978 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-31978 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31978?: CVE-2021-31978 affects Microsoft Malware Protection Engine. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-31978?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-31978 published?: CVE-2021-31978 was published on 2021-06-08 and last updated on 2026-06-17.

References

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

Affected products (1)

cpe:2.3:a:microsoft:malware_protection_engine:*:*:*:*:*:*:*:*

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