CVE-2021-33745: Windows DNS Server Denial of Service Vulnerability

Severity: medium (CVSS 4.0 v2.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-07-14 · updated 2026-08-10

Description

Windows DNS Server Denial of Service Vulnerability

Affected products

Microsoft Windows Server 2008: r2-sp1
Microsoft Windows Server 2012: r2
Microsoft Windows Server 2016: 20h2, 2004
Microsoft Windows Server 2019: all versions
Microsoft Windows Server 2008 R2 Service Pack 1: from 6.1.7601.0 before 6.1.7601.25661 — fixed in 6.1.7601.25661
Microsoft Windows Server 2008 Service Pack 2: from 6.0.6003.0 before 6.0.6003.21167 — fixed in 6.0.6003.21167
Microsoft Windows Server 2012: from 6.2.9200.0 before 6.2.9200.23409 — fixed in 6.2.9200.23409
Microsoft Windows Server 2012 R2: from 6.3.9600.0 before 6.3.9600.20069 — fixed in 6.3.9600.20069
Microsoft Windows Server 2016: from 10.0.14393.0 before 10.0.14393.4530 — fixed in 10.0.14393.4530
Microsoft Windows Server 2019: from 10.0.17763.0 before 10.0.17763.2061 — fixed in 10.0.17763.2061
Microsoft Windows Server version 2004: from 10.0.0 before 10.0.19041.1110 — fixed in 10.0.19041.1110
Microsoft Windows Server version 20H2: from 10.0.0 before 10.0.19042.1110 — fixed in 10.0.19042.1110

How to fix

Upgrade to a fixed version: Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25661; Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21167; Microsoft Windows Server 2012 6.2.9200.23409; Microsoft Windows Server 2012 R2 6.3.9600.20069; Microsoft Windows Server 2016 10.0.14393.4530; Microsoft Windows Server 2019 10.0.17763.2061; Microsoft Windows Server version 2004 10.0.19041.1110; Microsoft Windows Server version 20H2 10.0.19042.1110. Check the vendor advisory for mitigations.

References

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